Well first of all, I do have magnetic cock ring but not magnetic ball sack stretcher. I do know what you are talking about. For ball sack stretching, I would work with bolt on or USSR unless silicone and metal hybrid ever mature properly in the future. The reason magnetic have that problem is because to open the piece you push laterally not vertically and it have to be that way otherwise user would get injure. With lateral system to open, the problem is that when your sack contract, it is moving in the same magnetic field direction which leave small threshold of disengage than goes back and that is when pinch occurs. As for earlier thread, a member mentioned about how wife feel, well I am very explorative on multiple subject, in the beginning she have question about them, however, once my ball sack stretching result starts to kick in, she actually like it because I am able to give her even better orgasm during sex by doing this stretch.