The KZ ZST is a very popular budget-friendly IEM which retails for about 20USD. It’s ok. I specifically got the colorful candy version, not the all black version. I’ve heard there’s some difference between the two, with the candy being superior.
The build quality is good; the housings feel quite sturdy, and the cable, while annoying, does not feel like it is going to fail anytime soon. I cannot complain about the build quality of these IEMs.
I mentioned that the cable is annoying. The cable is extremely microphonic, with any motion of the cable exploding into a torrent of noise in my ears. The cable also is very rubbery, leading to it feeling quite cheap. It also has awful memory wire, which I had to remove, and I recommend everyone do. Fortunately for the sanity of anyone buying this IEM, the cable is removable, terminating in a 2-pin connector. While some would say 2-pin termination is a pro, I consider it a con, as, this being the only 2-pin IEM I own, I do not have any spare 2-pin cables on hand to replace this frustrating cable with.
Comfort is very good, once you get new tips. The tips that came with the ZST had a pattern of ridges around the opening, which irritated my ear canal, forcing me to use the silicone tips that came with my KZ ATE. The stock tips leave me wondering why they would make them.
The sound of the ZST overall sounds a bit off to me. The bass is quite light, lacking much impact. While bass notes can certainly be heard, it just does not come up enough to sound good. The midrange all sounds off. I have struggled to figure out what exactly is going on with the midrange, as some vocals just sound hollow and soulless, but some vocals can sound pretty good. Instruments can also sometimes sound horribly soulless, but other times sound fine. I do not understand the midrange of the ZST. There seems to be an elevation in the upper midrange, but that alone cannot account for the hollowness in some vocals. The treble is where this IEM shines however. The treble is certainly elevated, but not excessively so. Everything in the treble region sounds nicely defined, with plenty of detail.
All in all, the KZ ZST sounds weird, with the treble being the only aspect I enjoy. For 20USD, I cannot recommend these, especially when the Tennmak Pro is only 10USD more.