Karl,
Depending on the thickness of the screen protector, it can affect the iFly sensativity. If you are using a stylus or you fingernail with the no responce, the nushield that you reveiced won't work with it. They do make a few types of film, last I check. As for protecting the Screen of the iFly, this is not really necessary as we us a very durable screen. Many use there fingernail as we do with not damage at all. I would not recommend screen protectors for the iFly, it's screen is not like the consumer grade phones and devices that scratch very easily. We've tested several different films from NuShield, 3M and InvisiShield an really do not seen any improved results. The iFly offers better durability that most of these without degrading sensitivity or viewability. I hope this helps.
Thanks,