Don't know what's the hype but ZEX have decent reviews on youtube and I also read some reviews on aliexpress and some say it sound better than ZSX & ZAX, and ZEX sound like $150-200 IEMs.
The ZEX are
good for what they are, but they definitely do not sound like $150-200 IEMs. (source: has a $150-200 IEM)
Edit: That statement is perhaps somewhat unqualified, so let me clarify what I mean:
Test track: メビウス (Mebius) - めいちゃん, CD rip, ALAC
Setup: iPhone 12 -> Earmen Eagle, volume matched by ear
ZEX (purchased for USD 22)
Bass notes sound somewhat diffuse
Instruments and vocals are in the same plane in terms of depth, although there is *some* width
Vocals sound a tad flat and one dimensional, there's not enough resolution
Cymbals lack snap, are a bit vague
A4000 (purchased for USD 163)
Bass is less in quantity but sounds tighter, faster, kicks harder
Male vocals have depth, subtle details, bloom, forward presentation
Layered soundstage, each instrument occupies a different front-to-back position in addition to width
Cymbals are crashing, shimmering, sharp attack and decay
So... well... the ZEX are fine for the price. I intend to convert mine into budget TWS IEMs for exercising with. But even the Aria sound better if you're really paying attention.