Just received these last night. Here's a few first impressions:
They have plenty of volume headroom for me. Lots of power in this little DAC. The cable and enclosures are decently well made, and the case is nice. Just a bit above the level of quality I'd normally expect from the MSRP on these.
As for sound: These are ported dynamic driver earphones, so they actually have a pretty good wide soundstage, though it's not as tall sounding as others. I'm actually very impressed with the amount of sense of space these manage to impart. The highs have the emphasis in my pair, though I have heard from other people that their pair was muffled and bass focused? Maybe a design change? Maybe QA? Regardless, the highs are what stick out for me, and they're plentiful, but not extremely detailed. They're competent, but not where one would hear new things from old tracks.
The mids are sort of strange- the vocals are somewhat boosted, but the upper mids seem to be recessed, to the degree that they kind of leave the treble just hanging out there in space. These would be great headphones for phone calls, if they had a mic. The midtone detail is pretty decent, despite the vocals sounding a bit forced.
The bass has good extension, but (in my pair) is somewhat downplayed. If EQ'd they can pump out the beats pretty significantly, though they aren't as tight as I'd like to hear.
Overall, I'd say the Z:ero's are a neat concept, and if they could clear up the treble, they could be pretty respectable. I like the novelty of having a USB-based earphone for if my headphone port breaks on my phone, but I don't think that most of today's phones would be terribly improved by having this particular pairing of DAC and drivers. As far as interfacing is accomplished, with my Moto X Pure, they fit right in and worked almost immediately. This goes for the HTC M9, as well as the Samsung S6 and Note 4 that I've tried them with. Windows took a couple of minutes to recognize them and download the drivers, but the process was accomplished automatically, with patience.
The Z:ero's sound signature is similar to the RHA T10i, though they sound a good bit more veiled in the highs. Feel free to reply if you have any questions.