Depends on whether you want proper protection or not. Personally I always use Zagg (zaggDOTcom) screen protectors. Search for Zagg test on Youtube, its damn good stuff! Expensive, but worth it if you love your device!
I bought and installed the full body shield on one of our Trophys and screen only on the other; they are made by http://invisiblephoneguard.com/ and I got them both on Ebay for about $20 total. IMO, they are of the same quality as Zagg products but are substantially cheaper. If you search for IPG Trophy, you'll find it.
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