Some brief initial impressions.
Build quality is excellent at this price range, was a little smaller than I was expecting so that's a bonus. The new included is a real nice touch from Fiio when you consider how much they can cost.
Android interface is pretty good to me, reasonably snappy most of the time, a little quicker in tasks than what I remember of the Cayin I5, seems more stable as well.
Out of the box it detected a OTA update and installed it within minutes - very impressed with this.
Wifi - this is quite a biggie for me as I like to stream Spotify and radio on a fairly regular basis. The Fiio X7 was a letdown for me with some terrible interference when streaming, the Cayin I5 was a complete non starter, had 2 of them and neither managed to stream radio or give stable connection to Spotify and wouldn't work with Tidal.
The wifi on the X5 so far seems quicker with no interference when I've streamed from Spotify or radio apps, downloading and streaming from my NAS drive has been flawless as well. Something the I5 couldn't seem to cope with although maybe these issues have been resolved now.
Sound quality seems very good so far, only had a couple of hours with my Flare R2pro and B&W P9 and they both sound pretty awesome through the X5, will be trying out my Fidue A91 in balanced over the next couple of days.
So far very impressed with the X5, got it for a good price from AMP3 with a little bit of cashback from TopCashback which helps sweeten the deal!