I didn't care for the slightly tacky feeling of the screen InvisibleShield screen protector and sent it back for a refund. I'm a big fan of the crystal screen protectors that Apple handles. You can hardly tell it's there, and it feels like the naked screen.
YMMV, though. I am sure it does a great job of protection, and I use them on two digital cameras without trouble. Just not on the front of my iPhone.
bestskinsever(.com) is exactly the same thing as the zagg shield, but costs half as much (I got one last month and it's great).