UM2

KZ exploded on to the scene as being one of the first affordable IEMs. I have Westone UM2 Pro and they cost 10x as much and I still think the KZ work better. A big thing is that musicians aren’t listening to mastered audio, we’re listening to raw instrument sources uncompressed, so a lot of dynamic range and headroom is key, and a 5 driver IEM will do that. Also when you’re gigging/ touring your gear is going to take a beating. Especially since IEMs are so small. They’re easy to loose, step on, or drop in a beer. Getting cheap ones means their easy to replace in case something happens.

Gigging bassist here, I use Westone dual driver IEMs. The model I have are no longer produced, they are probably closest to the ProX20's. They have good sound isolation, good frequency response and are comfortable to wear. I'd buy them again, not cheap but worth the money IMHO.