Before I start with the review I'd like to note that I'm not big on audiophile terms. As such, I'll try to limit the use of terms like "bright" or "sound stage". I have done a bit of semi-professional sound engineering and environment setup. With that out of the way on with the review.
Sound quality: In a single word great! I’ve tested this unit with a variety of over the ear headphones, IEMs, and compared this to a variety of other amps, and DACs. Initially, I was suspicious of the XBass and 3D sound settings. Typically the choice of speaker or headphone in this case determines a lot about the sound you get. Some earphones are bass heavy, some have harsher treble, some have a relatively flat frequency response. For an example of what I mean google goldenears and lookup a few popular headphones. Given this, you typically just want an AMP/DAC to give you a flat response in order to not get in the way, or to over accentuate various characteristics. In this case however I’ve found that I could make even the most boring and flat headphones sing with a various combination of filters / effects. The 3D sound -- to my ear -- offers a slight treble boost while adding a tiny bit of reverb. This gives a sound that is a bit like using a open back headphone or like you’re listening to your music in a room with nice acoustics. The XBass is just a modest boost of the very low ranges with can be a help for headphones that are lacking in the thump department. The filters help with some of the phase problems you get with digital music which eliminates some of the harsh characteristics you get out of a digital AMP. The great thing about this setup is that if you want a great sounding flat AMP/DAC you can just leave it at the defaults and it get the best of all worlds.
Build quality / hardware / accessories: The unit is a solid metal chassis with some particularly solid switches. Given that this is a portable unit I'm a little unsure how the protruding volume knob and XBass / 3D sound switches will hold up if the unit is roughed up, but they feel extremely solid. The unit is a little longer and more narrow than my phone (Samsung S3) it seems like it’s about iPhone width.. In the box you get a couple straps for your phone, a rubber pad to prevent scratching, some rubber feet, a USB 3 cable, a ¼" headphone adapter, a couple USB adapters, a short headphone patch cable, and a fuzzy black carrying pouch for the unit. It would be nice if they offered a USB OTG cable as well, but it has everything needed to use the device in almost every circumstance already included. Over all I’m satisfied.
Customer service: Unfortunately, due to the tracks and setup I used I ran into a firmware problem. After I realized and tracked down the problem to the iFi product I ended up having to work with the tech support team there. While it did take awhile to track down (as the problem was pretty odd) the support team was responsive, and cordial throughout the process. Eventually we got everything sorted out during which time the team went above and beyond what I would typically expect. I typically don’t review many products, but with the service I’ve received, and sound quality offered, I felt compelled.
Conclusion: If you want a solid unit that sounds great with virtually every IEM or over the ear headphone, from a company that stands behind their product and has great customer service -- look no further.