A little background to HOW I ended up buying the xDSD:

I've been searching for a capable hybrid mobile-desktop solution for years, already. I've had some success, but was never truly happy with the choices I've had. I've been through a bunch of Fiio products, Qudelix 5k, Audioquest Red and Cobalt, and even the cheaper iFi hip-dac. But now that I've had the xDSD for little over a week, it is indeed (ALMOST) what I've been searching for, and overall the best out of everything else I've had (true, it is the most expensive, but I got it at a discount for around 300 euros vs 400).

One very important thing to note is that I'm searching for a DAC/AMP that offers excellent sound quality (primarily), and NOT huge amounts of power, since my listening device is an IEM (Campfire Dorado 2020) which is quite sensitive and requires very little power.



1) Excellent Sound Quality:

Sound quality is relative to what you compare it to. And I've compared it directly to 5 sources, which I will list here in from best to worse in terms of sound quality (not power):

Audioquest Cobalt (usb DAC/AMP dongle)
Audioquest Red (usb DAC/AMP dongle)
Xperia 1 mark 2 (smartphone)
Qudelix 5K (bluetooth DAC/AMP stick)
Fiio BTR5 (bluetooth DAC/AMP stick)

I will not go in details regarding each and every - but in short, I was searching for something that definitely sounds better than my smartphone's 3.5mm output (Xperia 1 mark 2) so that I can have great sound from my laptop as well. I'll compare it to the Audioquest Cobalt - and the comparison is pretty easy:
It has more authority in the lower registers, more rumble in the subbass, slam in the upper bass, and more heft to the vocals. It's warmer, has sweeter trebble slightly rolled off, but where the cobalt has crispier highs, the xDSD has a wider soundstage and grander presentation. The separation is about equal, but the xDSD sounds definitely more musical. Funnily enough, when switching the xDSD to "measure" mode, it sounds much closer to the Cobalt.

As far as the 2 extra functions, Xbass+ and 3d+, from my point of view they have the following functions:
xbss+ - this should be used if your headphones lack a bit of heft in the lower registries. I see no point on my Dorado 2020 since it has more than enough bass, but it can be a great function for headphones with weaker bass response
3d+ - this seems to do 2 things, making the soundstage narrower but taller, and elevating the trebble. It can make some songs sound a bit shouty, but again, i think this is useful for headphones that don't have a great soundstage - it also seems to take away a bit of separation

As for the listen/measure switch on the back, it seems "measure" makes the sound a little bit more flat and less exciting. I see no reason for ever using it.

Matching - this seems to be great for IEMs, but I will note that for my Dorado 2020s (10ohm, 94db/1khz) has a TINY TINY amount of hiss - not enough to bother by ANY means. I did try out the iFi IEMatch+ - it completely silences the hiss, but it has 2 disadvantages: it seems to make the soundstage a tiny bit narrower, and because you need to crank up the volume due to the attenuation, in bt mode you will end up with a shorter battery life. For anything more sensitive than what i have, the hiss might be a bit of a bother, so maybe avoid or use the IEMatch (especially if you're not planning in using the BT function on the go).



2) Beautiful design

I see a lot of people saying that the design is "bad" because it's a fingerprint magnet. What isn't a fingerprint magnet these days? My ceramic Dorado 2020s are fingerprint magnets (but you gotta admit, visually, the Dorado 2020 + xDSD work perfecly, almost the same color), my Sony Xperia 1 II (and many other smarpthones) is a fingerprint magnet. I don't feel like that's such a big minus.
On the upside, it looks gorgeous, unique, from the magnesium alloy case to the led-illuminated volume know which changes color according to volume level. I just like it, and it's small and light enough to be great on the go.

3) No-nonsense layout

It's rather simple - on the front you have a jack, the color-changing infinity-spinning (but analog circuit) volume knob, and another multifunction button for bt pairing/3d/xbass.
On the rear you got a usb-c (for the 2019 models) for charging, iFi's strange but very solid male USB port for data, a listen/measure swich and a SPDIF. Nothing is too much or too confusing.



4) Solid bluetooth connectivity, and quite possibly the best bluetooth SQ out there (even without LDAC)

Regarding connection stability - I have had NO issues. Be it in the house (5 meters and still no dropouts) or on the go/biking/gym (smartphone in one pocket, xDSD in the other) - I experienced 0 dropouts.
Regarding latency - it has less latency than the Fiio BTR5 and Qudelix 5k. I used it for gaming, and it's quite obvious.
Regarding bt sound quality - it's possibly the best. Why? I can't really explain, there's a very in-depth explanation on how iFi implemented the bluetooth and built it themselves, with a separate clock and circuitry to eliminate jitter and all of the bluetooth "bugs" that make almost any bluetooth device, even with LDAC, to sound too "digital" and bluetooth-y. This one doesn't, there's VERY little sound quality loss when using with bluetooth. Of course, you won't get MQA. The only element that probably is responsible for the -SLIGHT- SQ loss (generally less top extension and soundstage) is probably down to the aptX codec which will affect the digital info, particularly if you're listening to anything above mp3 320kbs quality.

5) Solid battery life

This is pretty straight forward to relay - I get anywhere between 7 and 7:30 hours when using on bluetooth (the only time I use it on battery). That's at around 60-70% volume, since that's very loud with my IEMs. That's solid. The other BT DACs i've tested, the Fiio BTR5 and Qudelix 5k, lasted for around 5 and 6 hours respectively.

6) Very versatile:

Well...you can use it as a desktop MQA capable DAC/AMP, which is probably the BEST DAC/AMP you can get, sound quality-wise, at this price, for your desktop (especially if you get it at a slight discount, 50$/EUR off), and then you can use it as a mobile bluetooth music device connected to your phone, which also is, I'd say, most definitely the best bt dac/amp you can get at it's price - especially since the only ones I know of, and which are much cheaper, are the Fiio BTR5 and Qudelix 5K - and the xDSD is simply in ANOTHER LEAGUE compared to those - no point comparing.

And now, we go to the CONS:

1) Bluetooth is not capable of handling calls, at all (no sound during calls or ringtone)

Quite simply, this is the single REAL fault with this device. It cannot accept calls at all. It has no on-board mic. 3.5mm cables with in-line mic do NOT work. When you get a call on your smartphone, you get NO notification besides the fact that the music STOPS (this is how you can tell that you're getting a call), and the sound of the call will not go through the xDSD, you have to use your phone to talk. This is valid for all types of calls - phone calls, whatsapp calls, signal calls, regardless of app. That's quite unfortunate. If (or..."when"?) iFi will launch a revised/next gen xDSD device, they simply MUST (no questions) include the call feature. Doesn't even matter if it doesn't have a built-in mic, it just needs to accept 3.5mm in-line mic connections. This will result in the absolute greatest "swiss army knife" type of product in the audio headphone DAC/AMP industry.

2) Had one bluetooth bug (had to re-pair)

This morning, the BT didn't work. It did connect, both to my laptop and smarpthone. But there was NO SOUND coming through. IDK why. I've tried everything, and the only fix is to unpair and re-pair on the source devices.

3) No music controls.

The only 2 controls you get for your music (usb or bt use) are volume, and mute (when you press the volume knob). There's absolutely no controls for next/previous/play/pause. That's a shame but not SUCH a big deal.

4) No OTG cable out of the box.

It should definitely include an OTG cable in the box. The Dragonflies have one, the Fiios, the Qudelix. Hell, even the cheaper iFi hip-dac has one. Simple as that.


So there you have it. In short, the sound quality is SOOO GOOOD that at the moment I'm using it on the go for every single activity - walks, going to the store, going to the gym - besides biking. And that's because it has no call handling and while it's quite acceptable to take out an IEM out of your ear, take out your smatphone and have a conversation on it when on the go/gym, it's very problematic when biking. And I HATE using TWS buds with much worse sound quality when biking. I want to use my xDSD. Please, iFi, make that happen in the next generation - CALL HANDLING.

10x!

After reading a few impressions, and using Fiio BTR5 for more than half a year (and being so unhappy with it that I relegated it to car use, in the meantime going through some other DACs) - I decided to order the Qudelix 5k and try it - particularly after reading that it was a Sony partner when implementing LDAC (this was interesting to me considering the HORRIBLE LDAC/BT performance on the BTR5)



In order to keep this this review concise, I'm going to simply expand each Pro and Con and elaborate:

PROS:

1) Best-in-class, refined sound quality and tuning

When doing a review, it's obviously crucial to have a reference or competitor to compare. In this case, it's none other than the BTR5. I got the Fiio more than half a year ago, and although I was excited initially due to the reviews and design - I grew to almost hate it really quickly - and i've been through 2 of them already. The BIGGEST issue I had with the BTR5 was the LDAC stability. When moving more than 4-5 meters from the source, and/or when going to the gym/biking/for a jog, and keeping my smartphone in one pocket and the BTR5 in another, it would simply be unusable - constant, constant cutouts. I've tried numerous suggestions and "fixes" online, I even exchanged it thinking it was a lemon - no luck, when it comes to BT stability in many conditions, the BTR5's BT implementation is in itself a LEMON. Another 2 things I never liked about it were the sound quality and heft.
The sound always felt blunt, with minimal tuning. It doesn't have the "refined" sound one would expect from a decent DAC, even tough it was rather neutral.
The design was also quite bad - in order to clip it on a shirt, you had to use the case, which was horrible since it already made a very heavy device for it's category even heavier and bulkier. And the disappointment was aggravated by the fact that the in-built mic sounded pretty bad, much worse than an in-line mic on a cable.

Enter QUDELIX 5K. I'm happy to report that in the past week since I got it, I've had 0 (ZERO) dropouts, even when using it on the bike or at the gym - either in a separate pocket than the smartphone or on the t-shirt collar. Besides that - the sound REALLY impressed me. Just to note - I have NOT played around or modified any settings, eq, etc - I just left it standard (DAC- Performance mode - not 100% clear what that means but it's the best setting).
To compare to the BTR5 - it sound MUCH more refined, wider soundstage, better extension. I was so unhappy initially with the BTR5 that I reverted to using the jack on my phone (Sony Xperia 1 mark2 - it has dual Cirrus Logic DACs + DSEE Ultimate sound upscaling AI tech) - though the phone had less power (which didn't matter for me since I've used 2 very sensitive IEMs - Campfire Audio Polaris 2 and Dorado 2020), the sound from the phone had more heft in the lower registries and better separation (which amazed me). I ended up getting a Dragonfly Cobalt for PC use, which was closer (but a bit better) than the phone output.
As far as the QUDELIX 5k - I can say without a doubt that it sound MUCH better than the BTR5 - not a BIT but MUCH. Also, compared to my Xperia 1 II output, it also sounds wider with more headroom, and it's VERY VERY close to the Dragonfly Cobalt, which costs 2.5 times more (the Cobalt has slightly better top-end extension and separation, you have to REALLY listen to it to realise). Suffice to say, I've already sold the COBALT since I have no use for it anymore.

This is valid for both LDAC sound quality, and USB-DAC sound quality, vs the BTR5. I know some people pointed out in some reviews that on the spec sheet, the BTR5 has some dedicated USB controller. How does that help? I don't know, there's no point for a "spec" since it doesn't translate in actual performance. Same story with measurements. I turst what I hear - the BTR5 with it's advanced USB Controller does NOT sound (at all) as good and refined as the Qudelix 5K when used as a USB DAC.



2) Excellent LDAC stability, even at max bitrate (990 kb/s)

Not much to expand more here - as stated at 1), it is absolutely excellent when paired with my Sony Xperia 1 II

3) Lightweight + compact size, in-built metal clasp

This is a HUGE plus, especially over the BTR5. I can now easily clamp it to my t-shirt collar when doing sports activities, and this is all I really needed (as stated before, the BTR5 with the clasp-case was huge and very heavy). This way I can use whatever cable I want, even experiment with balanced, since I'm not forced to use a cable with in-built mic mmcx cable to be able to take calls with the BTR5 - and then when I "jailed" the BTR5 in the car stereo, in order to take calls with my phone (since Campfire Audio headphones, besides the Comet, don't come with a mic), I had to buy a new cable with in-built mic.



4) Very solid app with "transparency" mode and parametric EQ

There is not comparison with the "basic" Fiio app here. The app si excellent and lets you adjust a lot of things. 2 very crucial features, which you cannot find on many (or any?) other such companion apps for BT DACs are the Parametric EQ (I don't need it at all, but some might, it can even transform certain headphones that have issues), and the Transparency mode, AKA "Mic Pass-Thru" (which is amazing). Basically this is like any transparency mode that you can find on most NC headphones (like Sony, Bose or Apple). It lets you adjust how much sound to let through, and is VERY useful when going for a run, on the bike, or even in airports when listening for announcements (this is complemented by the fact that it's light-weight with in-built clasp and can easily be clamped to the t-shirt collar or such, even when doing sports). One small criticism here is that it doesn't seem to work if there's no music playing through the headphones - this is a small minus, and Qudelix should add the feature to always keep the transparency enabled, even if no music is playing - it can be very helpful.



5) Heaps of power for it's class, price and size

Not much to comment here - just check the specs. It has huge gusts of power (more than the BTR5). If you have smth hard to drive, this is your device. Not me though, my IEMs are quite sensitive and low-ohm.

6) Excellent Built Quality

Same here, not much to comment - even though it's plastic + metal clasp, the built quality is very SOLID. The BTR5 is also very well built.



7) Great mic quality

This is a huge + compared to the BTR5. The voice simply comes across as much cleaner and clearer, and you can even adjust it in the app. I can finally buy better cables (balanced also) and experiment without losing the call functionality like I did with the Fiio due to it's bad BT connection and mediocre MIC quality.



8) Great battery life

Simple - I get 1.5-2h more than the BTR5 on Performance + LDAC. that's around 7 hours vs 5.5 (BTR5). This is a straight forward PLUS.

CONS:

1) Buttons a bit flimsy/easy to press + weird location

It is what it is - even though the design is "cute" and the opposite red and blue led for each button looks nice (like a mini Blade Runner hover-police car), they are basically rocker buttons, and they don't have a lot of resistance when pressing - accidental presses are quite easy unfortunately. The location is also not great (on the top corners of the device...why??)

2) No display or button indicators

I personally don't care much for a display since I don't really need to look at it (and eats a bit of battery), but this is simply a feature that is absent on the Qudelix, but is present on the BTR5. Also, it has no button indicators at all.

3) Not water-proof in any way

This is not really a FAIR minus (no other device has IPX rating either, in this category, at least as far as I know) - but considering one of my use cases is doing sports with the Qudelix attached to the t-shirt collar, it gets touched by sweat from time to time, and sweat-proof rating would be a huge addition for reliability and longevity.

4) Although the packaging is nice and unique, a more premium unbox experience would go a long way for brand-awareness

I mean...look at it ) Check more online photos. Yes, there is some innovation there as it's sort of a origami-type technique to make the box so small, it doesn't really scream "cheap" - but having a much nicer box with some extras inside is what many people enjoy when getting a new device and unboxing it, it makes the experience memorable, and it's a very useful marketing tool for companies that want to build customer retention.
It can be argued that this is cost-cutting decision, and it can be justified, considering the device cost is in-line with the Chinese counterparts, but this is built in Korea (higher production costs). But considering the advantages, I think asking for 10% usd extra and shipping it with a premium box would go a long way and would help Qudelix more in the long-run.

5) OTA software update has some issues

This is something that needs to be fixed URGENTLY by Qudelix. Basically, in order to not have a FAILED update, you need to keep the screen open and the app in the foreground during the entire process. Switching out of the app or letting the phone go into idle mode (screen off) instantly freezes the update process, and you need to either repair or reinstall the app. Frustrating. On the other hand, it's not a minus vs it's direct competitior, the BTR5 - that one has no OTA update (as of yet) and needs to be updated in a very "oldschool" manner using a PC, and that also means you need to check the support page on the FIIO website from time to time to even KNOW if there's a new update. The Qudelix app instantly notifies you when there's an update.

6) No way to configure buttons and no way to access smartphone Assistant (Google Assistant/Siri/etc)

I consider this a big functionality omission by Qudelix. Almost every other product in this category (BTR5 included) has a way to map a button to be used as the Assistant activation in order to easily call someone when doing other activities (for example). NO such option on the Qudelix, you can't even re-map the buttons. I really hope this can be added in a future SW update - QUDELIX - PLEASE ADD ASSISTANT BUTTON MAPPING OPTION! 10X!

And that pretty much wraps my review. For reference, this is the gear I've used in this comparison/review process:

Sources: Laptop (USB) and Sony Xperia 1 mark2 (LDAC BT)
DACs: Qudelix 5K (duh!), Fiio BTR5, Audioquest Dragonfly Cobalt (sold)
Headphones: Campfire Audio Dorado 2020 (main), Campfire Audio Polaris 2 (for sale), Sony XBA-N1AP (sold)

I'll mostly present my review as to why I came back to these after almost 2 years, through the lens of the headphones I've owned in the meantime, since this might offer a different perspective, seeing as the internet is abundant of "classic" reviews.

I've had the WF-1000XM3 a while back (the first time), namely in mid 2019 when they came out, and I got them with my Xperia 5 smartphone. I had them after owning the WH-1000XM2 (over ear) and the MDR-1AM2 (over ear, wired).

At the time, although they didn't really match up to either the WH XM2 or the 1AM2, the freedom of true-wireless earbuds + functionalities was a big advantage. I liked the sound, but I always found the fit not that great, and the sound was i'd say a 3.5/5. It simply sounded a bit dull compared to what I was expecting, but it's very important to not that for some reason (probably Android's fault), back then, even with priority on sound quality and DSEE on, the connection was ALWAYS SBC, never AAC.

Half a year later I sold it and I've owned a few headphone since (especially after I got my Xperia 1 II smartphone, which brought back the headphone jack). The headphones were another pair of Sony 1AM2, quickly replaced by Sony N1-AP IEM, and later with a quite expensive pair of Campfire Audio Polaris 2 IEMs + Audioquest Dragonfly Cobalt USB DAC-AMP. These I've owned for quite a few months and I was very much in-love with the sound quality - they had an exaggerated bass response with excellent sub-bass extension, but very much a hi-fi sound.

At one point, recently, I simply got so tired of wires and decided to get some true wireless headphones to test vs the Campfire Audio - my goal was not to find something that sounds as good, because I simply wasn't expecting to find 2-300 USD bluetooth TW headphones to sound as good as wired 500 USD ones (especially in combination with a 300 USD portable DAC). I intentionally avoided the 1000xm3s due to my past experience, and went on a shopping spree - I ordered the Momentum TWS2, the Technics eah-AZ70 and the Audio Technica (forgot their model number).

After a 2 day comparison, I ended up keeping the Technics since I found them sounding better and more hi-fi (better sub-bass extension, more neutral sound, wider soundstage and separation) than the Sennheiser and Audio Technica. I actually found them sounding more open and more pleasing on different genres than the Campfire Polaris 2 (yeah, I compared them extensively) and was very happy with my decision - decided to sell the Audioquest Cobalt DAC and Campfire Polaris 2 IEMs, and have even change in my pocket.

After this short (long) story, the 1000XM3 starts to show it's face. The reason? Simple - I've been seeing more and more online recent comparison with the XM3s where people were comparing them (with the latest sf updates) to many other wireless IEMs, especially the Sennheiser, saying they sounded better. I had to scratch this itch and get it over with - are they better than the Technics?!

I found them heavily discounted (150USD) online at my local store, and ordered them, since I could still return either one after comparison (Sony or Technics).

And what do you think? After setting them up, it's important to note that unlike 2 years ago, the XM3s now connect to my Xperia phone via AAC, not SBC (this might be the biggest SQ change factor). After a few hours of comparing with the Technics I found the following:

The Sony have :

a much better and pleasing response across the entire frequency response, especially the bass and mids.
a much better noise cancelling, with no hiss, and very little affect on SQ comparted to the Technics (the Technics narrow the soundstage and introduce a bass bump)

In short, with the exception of the sub-bass extension which still goes to the Technics, the Sony sound hands down better, more balanced and more enjoyable, all the while having much better NC, better functionalities, and better comfort (although the Technics do have an IP rating).

So, in conclusion, I give the WF-1000XM3 a solid 5/5 in March 2021 (almost 2 years after launch) because, overall, they simply sound better and more enjoyable than:

1) a 500 USD "audiophile" IEM, the Campfire Audio Polaris v2 (ping me if you're interested, I'm selling them)
2) The Sony XBA-N1AP IEMs
2) The Sennheiser Momentum TWS2, the Technics AZ70 TWS, and the Audio Technica ANC300TW

Since they sound better than basically all of their direct competition, and in many aspects better than some 500 USD Campfire IEMs i own, + the much improved functionality and excellent NC (when it's needed, sound is better, wider and nicer with NC off), there's no way the XM3 are not worth -at least- 5/5 stars in 2021.

Important to note that I'm a 34 year old man, and I have very good hearing (tested).

All I want now is to see what Sony can possibly do with the XM4 since there area already leaks online .

A NOTE ON COMFORT AND FIT: I've been through quite some tips with these: Standard silcone ones, Sony triple comfort, SpinFit 360, Spin Fit 500, Final and Campfire Audio Foam tips. The only ones that fit me best for sound quality and especially stability are the STANDARD ones that came on the earphones, Medium-Large. And when I say that, I mean that with any other type of tip from all the aforementioned, the fit/stability and/or the sound suffered A LOT, negatively. So for example the Spin Fit 360 were horrible and sounded much worse, the triple comfort wouldn't stay in my ear at all, the Final ones the same with muffled sound, etc. Your mileage may vary, but for me, the standard ones (medium-large for my ears) are not the best, BY far the best, night-and-day, make or break.

Got this earphones for the sole purpose of working out/biking. Tested out multiple sports headsets (similarly priced), from sennheiser and bose. They tend to sound better, especially than the adidas sennheiser which sound pretty bad for the money. Great bass and clear mids and highs (considering it is bass-centric). 
 
It is not neutral by any stretch, but you have to remember they are made for sports and wokring out mostly, so they are perfectly tuned for dyamic songs, like hip hop and electronic music, which is what most people listen to when working out (hence the name, Sonic Fuel). For these genres, they work PERFECTLY.
 
The in line mic has a analog volume control button, which is good since you will be able to modify the volume regardless what brand your phone is. The microphone is also very good, people on the other side of the line heard me clear.
 
The downsides are, in my opinion, the cables which have a tendency to stick to each other, making them non tangle free. The volume/microphone module is placed rather slow, so if you wear them under your shirt when working out it's kinda hard to take calls. Also, it would have been a big plus if they were at least sweat proof.
 
However they deserve a 5 star rating in my opinion because for what they are made, active wear, they are incredible stable in your ear, and are almost flawlessly tuned for the kind of music one listens to while working out.