Honestly? Aside from my phone (Moto G4, so nothing special), I've only used the KZ ZST with my Fiio E07K. I like it well enough. I should try it with my Fiio Q1 mk II as well but I haven't been able to stop myself from using my Takstar pro 82 every time I use the Q1. The fully opened bass ports with bass boost is stupidly fun.
My experience with non-headphone audio is still heavily lacking. The only earbuds or iems that I have experience with are: VE Monk+, KZ ZS3, and the KZ ZST. Please don't let me overhype you. I like the ZST, the $18 base price is great, and they definitely aren't boring but I own or have heard multiple headphones I would choose over them.
In fact, I would choose any of these over the KZ ZST: Beyerdynamic DT990 600 ohm (with MrSpeakers Alpha Pads), Takstar Pro 82, Audeze LCDX, Philips SHP9500S, Hifiman HE-400I.
And I would choose the KZ ZST over these: AudioTechnica ATH-AD700, Sony MDR-V6, Superlux 668B (Brainwavz HM5 Velour pads), Sennheiser HD280 Pro, VE Monk+, Axent Wear Cat Ear LED Headphones (my girlfriend's set...), KZ ZS3.
At the price tag, I think the ZST is absolutely worth a try and very fun with foam tips. Just don't expect it to dazzle more than $200+ headphones or the stupidly good valued sets like the SHP9500S or the Pro 82.
Oh, and my desk setup is a Schiit Mimby/Magni 2 stack with a pair of Beyerdynamic DT990 600 ohm padswapped to MrSpeakers Alpha Pads. Portable is the Fiio Q1 mk II with Takstar Pro 82 but potentially with KZ ZST as well. My desk is definitely better in treble and bass (in cleanliness, sparkle, and impact) but my portable setup is pretty good too. The Pro 82 is a closed back with a detachable cable, comfy, light, and with adjustable bass. It's also pretty portable for an overear headphone. It also has that effect of enjoyable sound where you just kinda forget you're listening to music even while you enjoy it. Then bass or sub bass comes in and it's so very there. Absolutely worth ~$72 and the month to come in from china.