NiceHCK DIY MX500s in, been listening to them a bit today.
Tuning: I would call it mildly mid-forward (can be somewhat shouty at times) but with decent air and sparkle up in the treble. Decent bass extension for an earbud, I guess, but worse than even the worst of IEMs. That's a given, though. The relative lack of bass does make these sound very thin and hollow compared to an IEM, though, and instruments simply lack a lot of body. They respond well to EQ, though. You could add 3-4dB of midbass and they do handle it well.
Soundstage: Friggin massive for a tiny $10 earbud. It competes with semi open over ears I've heard, like the Samson SR850 I have. Very impressive. Certainly bigger than the KZ ZAX.
Detail retrieval: Decent for the price range. I've heard the KZ ZST which also go for $10 and I think these are slightly more resolving.
Imaging: Not awful but it is somewhat fuzzy and smeary. Definitely can't compete with multi driver hybrids.
Design: The MX500 shell is very very ugly to me. Nice paint job, though. I have the glittery blue ones. And a surprisingly good cable for, again, just 10 bucks.
Overall, these won't be making my IEMs retire anytime soon. But for $10? Excellent to have just for the amazing soundstage, or just for having a different form factor option. Money well spent even for an earbud skeptic like myself.