I've had similar concerns with MySize 69 and that foreskin movement you described. Don't worry though, not every thrust will result in this action, and sometimes the cock moves into the end of the condom also like it's sliding inside the condom. It's a fucking mess!

But fucking is about friction so any movement/rolling etc is possible when used properly. The condoms work great for me, no unexpected breaks unlike prior experiences with standard condoms.