I use the crystal anti glare film on mine as a fix for the commonly reported problem of the otterbox screen sticking to the iPhone screen causing a major "bubble" problem.
This proved to be an instant fix. Much better than the advice given to just rub natural body oil on the iPhone screen before installing.
It works because the texture of the anti glare film prevents the two screens from sticking to each other. I love the Otterbox case!!!
I do not use a film, but if the cases' film works while another film is on, I say go for it. I do not have the bubble problem now.....I used to, but it went away.