I am mechanically inclined but cannot get this unit to work on my watches.  Tried it on 3 and it scratches the back case each time, plus it only has 2 prongs so lining it up is very difficult and the tightening mechanism just doesn't get the prongs in place with any accuracy.  For the price I will not return, but I suggest you buy a 3 prong Opener, that is what I am doing.