I was convinced to try the Invisible Shield by a pushy salesman (Apple fan easily led, who'da thunk it?) and it lasted three days. Bad show.
First, these things are a pain in the neck to apply. The screen cover takes the patience of Job, but the rear cover looks like it was designed to increase the sales of blood pressure medication. After half an hour of fiddling around I gave up on it and threw it out, leaving just the screen cover.
After three days the cover was still mottled, but I expect this would have improved over time as it says on the box. This I could live with, but the cover also ruined the texture of the screen - it's very difficult to smoothly scroll with a flick as your finger stutters up the screen. It feels cheap.
Worst of all, though, is the fact that after just three days the screen was deeply scratched in several places. I've used several screen protectors in the past and they've always lasted at last a few weeks before developing any signs of wear. At £13.99 I expected to be impressed, but based on this experience I'll go back to my cheap £5.99 for 2 screen films.