I have both. I'm happy with ZS10 Pro. It has great comfort for my particular ear, almost like it was custom made just for me. The sound is fun, enjoyable, and non-fatiguing. However, after hearing a lot about the upgrade to C12, I gave it a try. To me, the fit wasn't as good, and I couldn't hear a discernible difference. The yellow does look nice, but so does the crazy zigzag of the KZ. There are those who will say the timbre of the ZS10 Pros are "off" on certain instruments in certain frequency ranges. The word is "steely" - and it has been repeated so often and persistently that there is now a (imho unfair) kneejerk association between ZS10 Pro and this word. To my ears, I don't hear problems with timbre. Maybe it's the genre of music I listen to. Maybe I have the ears of a 90-year-old former boxer. I've given away a C12, but still have two ZS10 Pros. So, if you're happy with ZS10 Pro, if you have a great fit with it, in my humble opinion -- which is imperfect, fallible and something you should definitely not follow -- you're really not missing out on the C12.