I have both. There's a lot of info on this thread http://www.badmintoncentral.com/forums/index.php?threads/yonex-duora-z-strike-2017.168949/ several other users have compared it directly with ZFII. My personal experience is in agreement with previous comparisons. It's true ZFII players can easily adapt to ZS. In brief, both their shape and hence aerodynamic/timings are essentially identical. With equal string tension, ZFII is more head-heavy so quite a bit more powerful in smashes. DUOZS is less head-heavy so can move quicker when blocking smashes etc. I tried roughly comparing their balance point on finger simultaneously and there is quite a difference (~1-2cm) at the base of grip. These are the most significant differences for me. Other differences like ZS/ZFII backhand speed were less obvious. One personal note: love the matching lines on the ferrule.
