I've just partially installed the invisible shield, and of course, once installed the film over the screen I've not been able to resist making a scratch test (with a nail and a key) to verify that there were no marks, as stated in this promotional video:
http://www.youtube.com/watch?v=bJH3xZ5ZDwE
but to my unpleasant surprise, all the surface is scratched:

So, what the hell?