I got this just the other day (independently, not via Massdrop). Some first impressions without audiophile catch phrases.
Coming from a Fiio X1, this OS is clunky. Can only browse by folder. That is not how I sort my music. I keep one master file, with subfiles for each album. The X1 could sort in numerous ways, but grouping by artist has always been my go to. Having (6) Mare Cognitum folders (one for each album) makes browsing tedious. Add the fact that it is button click versus a scroll wheel and you are hitting that button often. At least it has a "page down button" to make it a bit faster, but not as fast as grouping by artist.
Other minor things like not remembering your browsing location if you back up or go into the track are a nuisance, but would be less so if browsing weren't so tedious. Also, not even a basic cover art display?
I'm really they fix that with firmware (I'm on the newest 1.06) because this thing sounds amazing. I "splurged" on some KZ ZS5 quad driver buds and a 2.5mm balanced cable for them. The KZ's with the stock cable really made me smile with the X1, especially for the 35 smackers they cost. When paired with the balanced out on the Aune, I didn't want to stop listening.
While the Fiio sounded great to me, this sounded more greater (intentional). The sound was fuller, more full of life. Bass had punch, not boom. Being a metal fan, that's right up my alley.
I'd recommend this based on the sound. If you are nuts about your OS, you will more than likely feel this device is lacking.