I've owned 2 of these. I really loved them (hence the 2), but both of them got unrestorable software issues which made the screen graphics go beserk and no way to reset it back to factory defaults.

So, that was it. Not worth it to go for a third attempt.

In terms of sound (AM2 module) i like it every bit. It's that Fiio sound that i like so much, even better than before on the X3.

The whole reason this product turns out to be a disaster is the software. Not only the very un-user friendly way of having to dig through Fiio's forums to find beta software updates (in 2 years there has been 0 stable releases) and complicated processes to upgrade. The software itself doesn't work well too. From annoying popups that makes the device unusable on 1 firmware version (the stable one) to beta versions that can't even store your saved (offline) spotify tracks. (it does save, but after a restart of Spotify/player it's all gone - the data is still there, filling up your free space, but unusable).

The only thing that works well is, like on any Fiio, using their player and play mp3's from the SD card. Which is not why i spend so much on a Android driven Fiio to have all the modern advantages it can't deliver.

It's really been a disappointment and i'm looking forward to replacing it. Also it's been my last Fiio. Mostly because posting my issues on the Fiio forum, not one Fiio employee even took the time to respond. Support = 0.

The sound in general is quite sparkling, open and well balanced for a single driver IEM.
The first thing i notice is that the bass is a little flat and lacks a bit of depth compared to high-end multi-driver IEM's. It doesn't have that good punch, warmth or layered experience most high-end IEM's possess. 
Update: the bass does seem to be better now, could also because of a better fit i've found. 
Once the music evolves to more complex compositions it's losing it's composure and that's were you notice most these are $30 headphones.
 
But listening to more mid centered music (singer songwriter stuff etc) is where these LG's shine. It's open,crisp and clear without getting harsh highs. 
It's the area most of these cheaper IEM's get either harsh or veiled, but the LG's are great for this. 
 
The soundstage is ok, not very wide, but natural sounding, it lacks depth and layers though. It just lacks some involvement in presentation. It's clear, but somehow just out of reach. The sound comes from a few meters away, where good high-end phones create much more intensity where you feel you can touch the music. 
 
The comfort isn't great for me with the supplied tips. They irritate quite quickly. But you can fix that with comply tips for instance. 
Update: tried with smaller tips then i usually do and now the fit quite well. Light irritation, but something i can easily wear for a few hours. 
 
The design is pretty good. The way they shape in your ear gives a very good seal. They do stick out slightly, which i don't prefer, but most IEM's have this issue. And they look nice too. The flat cord looks solid enough without losing flexibility.
 
Isolation is superb and works very well, considering i usually user custom tips for my #1 IEM, the Audeo PFE-232's. 
 
All in all, the positioning, experience and presentation is pretty darn good considering the price. They are open, but don't get harsh and therefore have a laidback sound without losing it's timings which is easy to listen too.
 
For me it's the lows that are the weaker part with these QB2's. They have something veiled over them and lack real depth and low frequencies, making them sound a little dull. It just lacks the real timbre and quality of instruments the high-end phones deliver. But then i'm talking about multidriver €400 - 500 headphones, so there's no way you can compare these.
 
Although in some areas they come quite close to my Shure SE535's, which says something. Actually, i prefer listening to these The Shure's are too harsh for my taste.
Comparing it to my Phonak PFE-232's it really becomes very clear though. That's a no contest. It's not in the same level.
 
For the price a no brainer if you're on a budget. For me it's a nice backup IEM for emergency's  

Not to repeat myself. You can read the review/comparison here:
http://www.head-fi.org/t/605222/review-phonak-pfe-232-vs-shure-se535

Well, i won't make a long review.
Having the iPod Nano V6, SansaClip+, SansaClip Fuse, iAudio 6 and a mix of older Sony's, iPod's etc ... I think the best sounding player to me was the iAudio 6. Followed by the iAudio J3. The difference is marginally, but somehow the 6 just performed a tiny bit better to my taste. The BBE+ etc effects just had a smoother and warming impact, where on the J3 it starts to sound a tad more cool, in some cases even mechanical (hissing etc), where the 6 kept composed. 
 
But ... sadly, i only managed to enjoy the J3 for a few months when it died. The screen showed weird colors, like there was some graphic card issue and froze, it didn't respond to any button actions. Resetting, rebooting ... nothing. So i returned it, got a new one, after a few months ... the same happened. 
 
So i've given up on this model. Might try some other iAudio devicse, but i have no confidence anymore in the J3. 

I've written a review about it here:
http://www.head-fi.org/t/605222/review-phonak-pfe-232-vs-shure-se535
 
 

Considering the value these are fine in-ear headphones. The design is slim and classy. 
 
Comfort
They fit well and are delivered with enough fitting options for most people. The comfort is fine, but my ears do start to itch/irritate a little after a few hours.  They are small enough for lying on your head without getting too uncomfortable. 
 
Sound
The sound is full and solid, but the soundstage isn't very exciting. It still feels like you really have earphones in. They don't take you away. It's a little bass driven and mids / highs need some tweaking to get it right (personal ofcourse).
Highs become a little sharp when opening them up with the equalizer (iAudio 9).
Generally they are warm sounding earphones. 
 
But i don't have much reference material. The phones is used before were also entry level Sennheisers. And personally i prefered those over this one. (can't remembert the model no.)
Im now upgrading to a Shure SE535, so i'll update this post after i've had a listen to those. Although it's in a total different price range obviously. 
 
Noise Cancellation
This is the part where the CX400-II really shine. You get cut off from the world and all you hear is the music playing. At low volumes you can still here something a little bit, but compared to the other Sennheisers i had before, these really made a difference in this area.
 
 
Considering the price, these are very good earphones.