I bought a 32GB micro-SD card to go with it. I put a few albums on there, all was going well. The player recognised and played them. Great. A bit later I put some more albums on.
Several hours later...
I tried to turn on the player, but it was having none of it. Eventually I discovered you can hold the power button for ~20 seconds to perform some kind of reset. It appeared to spring back into life at this point, but I think it would be more accurate to call it undead.
The player now freezes on "refreshing your media". It gets past this if I remove the SD card. Apparently this is a common issue if you have ID3 tags that deviate from what the player wants (i.e. its parser is unfit for purpose). Whether this extends to flac/vorbis metadata, I don't know. But I have two micro-SD cards and they both cause the same behaviour, regardless of their contents (or if they are blank), so it's not that, the player is just borked.
The MTP protocol seems to have died too:
A problem has occurred with one or more user-mode drivers and the hosting process has been terminated. This may temporarily interrupt your ability to access the devices. The device MTP USB Device (location Port_#0006.Hub_#0004) is offline due to a user-mode driver crash. Windows will attempt to restart the device 5 more times. Please contact the device manufacturer for more information about this problem. This device cannot start. (Code 10)
Rating: not so good.