I use Zagg on all my devices for years now. From experience, it will stretch if you reapply it too many times but it will still work overall.
People still don't believe me about how scratch resist they are so I show them. Pulled out my keys and went to town on screen. One of my friends started to freak out and screaming at me cause he didn't know about how good Zagg is. I still give him a hard time about it.
Bodyguardz is where its at. Zagg still has yet to fully get rid of the orange peel feeling on the phone, you can even see the orange peel texture on it..sad. Bodyguardz is smooth, and not to thin to where its going to peel off like my zagg did on my tbolt. Had it installed for about a month and this **** happens...sigh. Had a bodyguardz on my pre and couldn't even tell it was on there. Only reason I picked up a zagg is cuz I was in best buy right after I got my phone so didn't want my screen to scratch. Now I'm not using one anymore cuz I like the feel of the smooth screen, specially using swype.