They are completely clear, and the heat produced by the device doesn't seem to affect them. Like I said, I'll post a detailed writeup of this on my chintzy home page soon. Please be sure to post when you have it ready. Fred, I have been using the Casio screen protectors for the last couple of months. I am having a minor problem with the Casio brand protector slightly moving around on the screen.
Dirt can definitely get under the protector and on to the screen.
I haven't used any other yet because I still have a few of the Casio brand remaining. I am not dissatisfied enough with them to throw them out. These seem fractionally too big and don't sit flush with the screen.