Received my ZS10s. Had them them burn in for a week using the 1More Assistant app: https://play.google.com/store/apps/details?id=com.onemore.app.smartheadset.android The thing I find with CIEMs is that they require some good burn-in before they sound any good. I had this experience with the 1More Triple Drivers, 1More Quad Drivers, Mi Hybrid Pro HD, KZ ZS10 and i-INTO i8. I own a pair of UE900s and have had them burn-in too, but there was no difference in sound. While I could just listen to them as I burn-in, I have found that to be ineffective. I usually listen at 9 (on Sony NWZ-A17) or 20 (on Shanling M3s), volume levels. The burn-in app burns them progressively at multiple volumes (20-60% volume) using music and noise, over 5 days. I usually give them an initial listen (an hour or so) then set them to burn-in. I do not listen to them during burn-ins. 1More recommends their customers to perform burn-ins too. I do not have access to any audio test equipment and can't scientifically verify any of the above. But if you do and could do it, that would be great. Now onto my brief review. On initial listen, the ZS10 were: 1. Mids are recessed, almost non-existent, muddy. 2. Pounding bass, gave me a headache. 3. Treble sounded artificial and harsh, but not piercing. Kill4me (Mystery Skulls Remix) was painful to listen to. 4. Vocals sounded husky on almost every music I sampled. 4. Some instruments, like claps and cymbals, sounded fake/artificial. After burn-in: 1. Mids are slightly recessed, but much clearer. 2. Vocals greatly improved, no longer husky. I could separate out the voices in Heathens (Twenty One Pilots). 3. Treble sounded much more subdued and smoother. 5. Instruments sound natural. Slightly artificial on some string instruments. A huge improvement here. 6. Thumping, but no longer pounding bass. But, bass quality no where near the i8. Fit: 1. Switched from 3-flange silicone tips to foam tips. 2. Better fit with foam tips, could not get them to stay in my ears using silicone tips. 3. Tested tips before and after burn-in. 4. Even with foam tips, they pop out of ears after a while. Music sampled: Heathens - Twenty One Pilots The Game of Love - Michelle Branch What You Need - Bring Me the Horizon Maria Maria - Santana Strangers - Portishead All Mine - Portishead Going Back to Strange - Still Corners Angel - Theory of a Deadman Blood Hands - Royal Blood Communication - The Cardigans Lovefool - The Cardigans How Bizarre - OMC I Wanna Be With You - Mandy Moore Lust for Life - Lana Del Ray Kill4Me - Marilyn Manson (Mystery Skulls Remix) Verdict: For the price, the sound on the ZS10 is well above its value. Is it a TOTL killer? Hell no. Is it a fun IEM? Yes. Would I use it as my daily driver? No. I find the fit issues are a huge step back and is what that holds me back from enjoying them. Also, due to the short nozzles, it pops out of my ears after a while. I am going to turn these into balanced, so stay tuned for additional impressions. Thanks for reading!