We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-09-21 · 7 min read · Independent comparison
If you want a hybrid IEM tuned for speed, detail and high-frequency sparkle with a lightweight ear-hook fit, choose erjigo KZ ZST X; if you need a metal-shell in-ear with a microphone in the box, higher impedance and a wider, more forgiving tuning, choose Kinboofi KZ ZES IEM.
• erjigo KZ ZST X – biggest strength: A 1BA+1DD hybrid with a dedicated balanced-armature tweeter (30095) mounted at the nozzle, a 10mm double-magnetic dynamic driver, a 20Hz–40kHz frequency range and a silver-plated 100-core cable.
• erjigo KZ ZST X – biggest trade-off: Very low 12Ω impedance and 107dB/mW sensitivity make it easy to drive but also quick to reveal hiss or noise from a poor source; the ear-hook cable routing is not everyone's preference.
• Kinboofi KZ ZES IEM – biggest strength: Metal in-ear housings with strong sealing, a detachable 0.75mm 2-pin 3.5mm cable, a bundled microphone version, three pairs of silicone tips and a one-year protective period.
• Kinboofi KZ ZES IEM – biggest trade-off: 24Ω (listed as 32Ω in the product data) and 112dB/mW with a 10Hz–20kHz range means it rolls off above 20kHz; the 80g listed item weight is notably heavier than the ZST X's 3g.
• Pick erjigo KZ ZST X if you listen to instrumental, electroacoustic, drum-and-bass or gaming audio and want maximum upper-frequency detail and a featherweight fit.
• Pick Kinboofi KZ ZES IEM if you want a metal-bodied monitor with a mic included, a cable you can swap freely, and a tuning that stays comfortable over long listening sessions.
The KZ ZST X is built around a two-driver hybrid layout. There's a 10mm double-magnetic dynamic unit handling the low end, and a 30095 balanced-armature unit sitting at the front of the housing to handle high frequencies. Placing the BA at the nozzle is a deliberate design choice — it shortens the acoustic path so less high-frequency energy is lost before the sound reaches your ear. That's why the spec sheet claims better "ductility" up top and a frequency range that stretches to 40kHz, double what the ZES lists.
In practice, that combination points at a specific listener. If your library leans on electroacoustic music, drum and bass, or dense instrumental recordings where cymbals, plucks and transients need to stay separated, this is the tuning that makes sense. The 12Ω impedance and 107dB/mW sensitivity mean almost any phone, dongle or controller will drive it to loud volumes without strain — useful for gaming, where positional cues live in the upper mids and treble.
The cable is worth a note because it's part of the design story: a 100-core silver-plated wire with Kevlar fiber in the core, which the spec sheet says improves transparency, separation and soundstage while reducing signal loss. Whether or not you buy every claim, a detachable 0.75mm 2-pin system means you can replace or upgrade the cable later, which is real long-term value. The ear-hook shape and soft silicone tips are designed to reduce outside noise and keep the buds locked in over long sessions.
Who should skip it? If you want a microphone built into the package — the ZST X's mic is listed as optional, not guaranteed — or if you dislike ear-hook routing and prefer a straight drop-in fit, look elsewhere. Also, at 12Ω this thing is sensitive enough to pick up background hiss from noisy sources, so a clean output matters.
The KZ ZES is the more conventional, more "finished" package of the two. It's a metal-housed in-ear with a hybrid driver setup, and its stated impedance is 24Ω (the product data lists 32Ω) with 112dB/mW sensitivity. That higher impedance makes it slightly less fussy about source noise than the 12Ω ZST X, and 112dB/mW means it still gets loud easily from a phone.
The frequency range is 10Hz–20kHz. That's wider at the bottom than the ZST X's 20Hz floor, but it stops at 20kHz instead of 40kHz. Read that honestly: you're trading some claimed upper extension for a tuning that's likely to feel smoother and less aggressive up top. For pop, podcasts, rock and general everyday listening, that's often the more comfortable choice over a long commute.
The housing is the headline feature. A metal shell with good sealing is exactly what you want for passive noise isolation — the kind that blocks engine rumble, train noise and office chatter. The spec sheet calls this out directly, and it's the practical reason to pick the ZES over the ZST X if you're wearing these on a plane or a bus.
Then there's the bundle. You get the earphones, the cable, three pairs of silicone tips and a user manual, plus a one-year protective period from the date of purchase. The mic version is available, so if you take calls or game with voice chat, you don't need to hunt for a separate cable. And the 0.75mm gold-plated 2-pin connection is stated to be compatible with the vast majority of 2-pin upgrade cables, so personalizing the fit or sound later is straightforward.
Who should skip it? If you specifically want the ear-hook, ultra-light fit of the ZST X, the ZES's in-ear shape and heavier build (listed at 80g for the item, though that likely includes packaging) won't feel the same. And if you're chasing the last octave of treble detail, the 20kHz ceiling is a real limit compared with the ZST X.
Side-by-Side: Which Should You Choose?
• Best for bass impact and "speed" → erjigo KZ ZST X. The 10mm double-magnetic dynamic driver is specifically described as tuned for electroacoustic, drum and bass material.
• Best for noise isolation while commuting → Kinboofi KZ ZES IEM. The metal housing and sealing design are the explicit selling point here.
• Best for calls and voice chat → Kinboofi KZ ZES IEM. The mic version is a stated configuration; the ZST X's mic is only listed as optional.
• Best for low-impedance, easy-to-drive use → erjigo KZ ZST X. At 12Ω and 107dB/mW it's the more sensitive of the two, though it also exposes noisy sources.
• Best for smoother, less fatiguing long sessions → Kinboofi KZ ZES IEM. The 10Hz–20kHz tuning with higher impedance tends to be the gentler listen.
• Best for a complete out-of-the-box kit → Kinboofi KZ ZES IEM. Three pairs of tips, a manual and a one-year protective period are included.
• Best for a lightweight, secure ear-hook fit → erjigo KZ ZST X. The ear-hook design and silicone tips are built to stay put and stay out of the way.
• Best for cable tinkering → either, honestly. Both use 0.75mm 2-pin detachable cables; the ZES explicitly notes broad 2-pin compatibility.
In my opinion, the erjigo KZ ZST X is the one I'd buy if sound detail and a light, locked-in fit are what I care about most — the balanced-armature tweeter at the nozzle, the 10mm double-magnetic driver and the silver-plated detachable cable give it the more interesting, more resolving design on paper.
But I'd steer toward the Kinboofi KZ ZES IEM if my priority list is noise isolation, a microphone in the box, and a metal build that feels substantial. It's the safer, more complete everyday pick.
So: ZST X for the listener who chases detail; ZES for the listener who wants a tough, quiet, all-in-one monitor. Check the current price on Amazon before you commit, since that's the part I can't tell you here.
Not universally. The ZST X wins on high-frequency extension (40kHz vs 20kHz) and sensitivity (107dB/mW vs 112dB/mW at lower 12Ω impedance). The ZES wins on isolation, bundled accessories and mic availability. It depends on your use case, not on one being objectively superior.
Based on the specs, the Kinboofi KZ ZES IEM. Its metal housing and sealing design are explicitly described as blocking ambient noise well, while the ZST X relies on soft silicone tips and ear-hook fit for its noise reduction.
Yes. Both use a 0.75mm 2-pin connection and a 3.5mm plug. The ZES specifically notes its gold-plated pins are compatible with the vast majority of 2-pin upgrade cables, so swapping cables is easy on either model.
The erjigo KZ ZST X, at 12Ω impedance and 107dB/mW sensitivity. The Kinboofi KZ ZES IEM sits at 24Ω (32Ω per one data field) with 112dB/mW, which is still phone-friendly but slightly less sensitive to background hiss.
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