I wouldn't worry about the invisible shield. I have never heard of anyone scratching their screen with the pen, etc. Well, except for one case where someone said they were using it at the beach and got sand on the pen tip, which caused a scratch. But not from just normal use.
iRex puts a protective coating on the screen already. The main thing you want to add is the impact protection that the cover gives. I wouldn't bother with any of the film protectors or invisible shields, etc.
|