Alright, the Shmci C4 arrived... it is in fact the Zero Monster H-10.
Can't find any info online about this brand or model. But the C4 was supposed to have the same DAC/AMP as the Nintaus x10, so... if this still has those internals... I don't know, but it sounds good man.
Listening now. I loaded it with all my MP3's (lowest production-quality music I keep as MP3 320) and it beats the Sony NW-E394 that my MP3's lived on handily in terms of sound quality. Clear and warm. Nice treble without getting harsh. Great percussion. Strong, sensible bass.
UI mostly works. Category browsing will shuffle tracks out of their album order, but file browsing works fine, and my music library is well-organised, so it's all good.