It had been a while since i gave a listen to the ES4. These are a gem to me. That pleasing boomy bass, present mids (very well done, some of the best from kz), highs that could be tuned better, but not unacceptable at all with good presence. Good pair with my smartphone. Obviously not geared towards neutrality or serious tuning. It doesn't throw music in your face like the zs7(with the upgrade cable) or zsn pro, rather just presents it to you. Perfect for casual listening and getting those reggae vibes on.
Tried on an upgrade cable that I bought for the zs7. I've been hooked since. Think this iem will go on as a future legend for me as much as the zst, ate and ed9 currently are.