Aluminum main body (front to the side) with a plastic back cover.
The UI works similarly to some of the mod UI on X5. It is still in early beta stage at the moment so I don't want to comment too much on it.
As for SQ - I don't have a stock X3 anymore (mine is mod'ed with AD8620) so I can't give you a comparison. But that being said, it is definitely on the warmer side of things, but it doesn't remind me that it is quite as warm as the stock X3. The actual SQ isn't as good as my mod'ed X3, but I think it is at least on par with any DAP on the $100 price bucket. For the least, I don't think it comes short compared to nano 7G or ColorFly C3. The only difference I can observe for now is that both nano 7G and C3 are on the leaner, more detail oriented side of the presentation where X1 is on the richer, tighter side of the presentation. The bass hit does come out much more pronouns on the X1, where they are often softer in tone in nano 7G or C3. The line-out is integrated into the same socket as headphone-out, and is selectable in option. It is actually quite clean and I think X1 will make for a pretty good source to feed an amp.
Please note that this is still an engineering sample, so it might not equal to what we will see on the retail version.