iFi Micro iUSB3.0 - Reviews
Pros: Inky black background to music, increased depth and width of soundstage, more natural note decay, can charge several devices at once at a fast rate
Cons: Sometimes forces restart of JRiver to re-identify DACs
I'll start off with an intro to me. I'm a 33 year old long time audio enthusiast that has only really started to get seriously involved in the audiophilia hobby in the last year. In that time I've picked up almost my entire collection of audio gear (more on that below). My music tastes are very broad, but don't include much main stream country music, EDM, or mainstream tween pop. It would not be an unusual listening session to for me to have Frank Sinatra in the morning, Amon Amarth at noon, with some Pink Floyd, Aesop Rock, Beck, Charles Mingus, and an awesome and obscure Japanese band called Boy's Age to round out the day.
My home rig consists of the following:
LH Labs Geek Out V2
Feliks Audio Elise Valve Amp w/ C3G driver and C13s power tubes
HD600 headphones
LH Labs Lightspeed 2 Split power and data USB cable
...and various interconnects and a shielded power cable for the Elise
I did not buy this iUSB3.0. I was lucky enough to win one through an iFi giveaway here on HeadFi, and iFi was gracious enough to get it to me very quickly so I could test it out with a top-tier DAC or two that I do not own. I was only able to get it hooked into the Schiit Yggdrasil, but I'll be getting my own high end DAC soon.
When I got this, my mother-in-law was here, there were presents for the new baby brought from across the ocean strewn all over and no space to take any sexy pictures of the packaging and contents. For those kind of pictures go to the iFi iUSB3.0 thread. I do have some pictures from a little meet-up where the iFi upped the game of the Schiit Yggdrasil. That's it in the picture below hiding behind the computer whilst feeding the Schiit Yggdrasil/Ragnarok stack some delicious tunes.

You can also hook multiple DACs up at the same time for quick A/B testing of the DACs and headphones. Below I've got it hooked up to the LH Labs Geek Out V2 and Geek Out 1000. The observance of another mini-meet goer was that it made the sound more refined. I agree, but there is more.

When I received the iFi iUSB3.0, I immediately tested it out with my favourite test track:
Katherine Bryan - Flute Concerto Alla Marcia
The track has a lot of stage depth and width, extreme differences in pitch, big tympani strikes, and incredibly fast well-defined flute notes that are a perfect torture test for seeing if you've got a treble emphasized piece of equipment.  Switching between the Geek Out V2 plugged into the computer using the Lightspeed 2 USB cable and fed through the iUSB3.0 via the included usb 3.0 cable with the Lightspeed 2 USB feeding the DAC, the difference was immediately apparent. The iUSB3.0 adds significant soundstage depth on my Sennheiser HD600 headphones, and a little bit of extra width. Drum strikes were noticeably more rounded and defined, the instruments were suspended in the aether with precise locations. When I switched to one of my favourite acoustic tracks, Tony Furtado - Angeline the Baker, the guitar plucks picked up a much more natural decay, bringing the feeling closer to live music.
I've listened to a lot of music through this now, and got the opportunity to do the same test tracks on the Schiit Yggdrasil to similar effect as the Geek Out V2. The Yggdrasil is incredibly resolving, and I was listening out of a HE-1000, which is also incredibly resolving, but it gave a little bit more depth and a nicer impact on drums and nice pluck on guitars compared to Yggdrasil without it. This iUSB3.0 is magic. I can't say I completely understand how it is working, but it is most definitely working.
Some additional music I've listened to: basically all of the Queen and Pink Floyd albums, loads of Led Zeppelin, Father John Misty, Black Sabbath, Massive Attack, Miles Davis, Fleetwood Mac, Boy's Age (very weird and very good), and some metal from my favourite metal band, Unleash the Archers.
I've used it to charge a couple of devices, my Note 2 and my DX50. It does what it says on the tin.
The main negative I've had is that when the music isn't flowing and I take my headphones off in a silent room, if I'm within 5 feet of the iPower, I can hear a high pitched sound. It is similar to the sound of my Samsung Note 2 charger whilst charging, probably up around 18 to 20k in pitch (I can hear 22k). Also, when I had this hooked in and a neighbouring USB slot was being used to transfer data to an external hard drive it made it sound like my system was broken--garbled interference crap all over the place. This was with the bog standard USB 3.0 cable that came with the iUSB3.0. I haven't tested it with my spare Supra USB cable as the interconnect between the computer and the iUSB3.0. Maybe a better made USB cable will make a difference, maybe not. I also found that I usually had to restart JRiver in between tests with and without the iUSB3.0. JRiver treats your DAC like it is a new DAC being plugged in when running through the iUSB3.0 for some reason I don't comprehend.
Overall, I'm very impressed with this little wonder. It boosted DAC function on DACs ranging between $300 and $3000 in price. I'm very happy to have it in my system and stopped doing comparisons pretty quick--the difference was that noticeable. I can't wait to show it off to more folks and try it out with my next DAC to arrive, the LH Labs Pulse XFi. I'd love to compare it to the Uptone Regen, but that will have to wait a bit.
Update 14/01/2016
The lovely folks at iFi contacted me to see how I was getting on with the iFi Micro iUSB3.0 and I told them I love it and I've only had the one issue. They took care of the issue immediately. They sent me a replacement iPower and now my primary complaint is gone. I use this with my Pulse X-Infinity (I got an upgrade) in my main system and the system is lovely. The pulse has a lovely stage and this only makes it better. I'm a big fan. Thanks iFi for your great customer service and great products! I hope every launch is a huge success! I wish I could have an iUSB3.0 on every system I have. Maybe I should get the iPurifier2 and see how that goes. 

I too have the iFi iUSB3.0 for about a month now and agree with most of your observations. Yes the background is pitch black with added width and soundstage. However if there is noise or hiss present in the recording itself it will not be eliminated, for example listening to Led Zep 4 Stairways I noticed some background hiss during the song's intro with or without the iUSB3.0. On very well produced tracks I noticed more details emerging like in Peter Gabriel's Don't Give Up towards the end the very faint background vocals of "don't give up" become very clear, something that I hardly noticed before. The downside to this is that poorly produced tracks will turn out to be obvious especially so if I'm listening to compilation albums where the inconsistency in quality between tracks can become very apparent.
Had no issues with high pitch noise coming from the iPower and no restarts required with the JRMC although in the beginning I had to re-install the driver 3 times before both Foobar and JRMC recognizes the hardware. Had to tweak the settings in JRMC before able to play DSD files natively with no clicks and pops which is better than using Foobar in comparison, but that's unrelated to the iUSB3.0 I guess.
Plugged in an external 1TB hard drive into the USB sound/power socket at the side and it immediately recognized the drive and works well to allow me to play the files from the expanded storage. All in all very satisfied with the product and looking forward to trying it with other USB DAC/preamp. Btw I'm using the iUSB3.0 with iFi iDSD and LCD-X.
@glassmonkey - was wondering about how good the iFi USB 3.0 was, principle of the iPower is very intriguing but basically it's the supplier of clean 9V power to the USB unit. Reclocking is what provides jitter free audio digital signal so if you can eliminate it, you suddenly get clearer sound. Has it's been said many times by different device builders, clean power and signal are everything. I find the price to be higher than a Regen but definitively prefer it's form factor. One added bonus is the fast 5 Gbps interface (USB 3.0). The only issue is you need a compatible 3.0 input port on your computer.

Thanks for a well written review and hope you'll be getting your Geek Pulse soon. Let us know how they pair together.
@musicheaven I got the Pulse X-Infinity and they play very well together. The noise floor is basically non-existent beyond that caused by having imperfect speakers/headphones. The X-Infinity is lovely. The sound is very 3-dimensional and it's clean and fast. Playing balanced out to my HD600 is dreamy.