I always install the Zagg InvisaShield on all of the touch screen phones my wife and I have had for years.
First, the protection it gives while in my pocket or (shudder) my wife's purse.
Second, it cuts down on the finger prints and smudges.
Third, it almost completely eliminates glare.
In the past I have always installed it myself, but for my Charge I had the girl at Best Buy do it. It took her about 15 minutes and in the end the film was too long and started to come off near the buttons within a couple of hours. I went back the next day and showed them the problem, they tried to fix it but in the end had to put on a new one. The whole thing was hassle free. I had nothing to fill out, nothing to return or mail in, just walked out with a perfectly applied screen protector.
I was told the second time not to put a case on for 3 days to let it cure, which I don’t remember reading but I think it made a difference in preventing the case from lifting the edges.