Greg,
I've been testing products from NuShield, 3M and others like BodyGuardz. I've even take a Nook protector (as they claim it's super "special for outdoor") and cut to fit, it works well too but nothing that stands out in the crowd. All seem to be very simple to install and hold up well other than the 3M, it scratched easy which was a surprise.
I do really like the BodyGuardz as it seems to have a really nice balance of light dispersion and Glare reduction without becoming to opaque in very harsh conditions. Once I've done a little more durability testing, we will likely be adding a screen protector option to the store.
The Zagg Invisibleshield is a great product, but seems to thick and tacky feeling for smooth operation on the iFly. It also is clear and has little glare-reduction. These work great for glass and polycarbonate screens, but not as well for the iFly resistive screen. Just a few thoughts.