Don't just rely on one person's view. Every one has different sense of hearing. I also have KZ ZS6 and I like it very much. I don't hear the heavy top end and serious lack of bass as described by crezo. By the way, I'm a classical musician with very good hearing.
The KZ ZS6 is still one of the best deals around especially at 26€. It has a good sense of stage and great separation, and It's dynamics and details makes you get lost in music. Great around all spectrum of frequancies. Better sub-bass, bass and mids than the great ZS5v1. I just love it.
I'm using comply tips and I sense no piercing treble at all. I'm 45 though, so maybe a 20's old ear is different in the treble department.
I tried almost all KZ's and dozens of others IEMs and the ZS6 is still one of the best (the best KZs for me are: ZS10 > ZS6 > ED16 > ED9 > EDR1).