If you already bought them, then go ahead and use them. It shouldn't harm your screen in anyway. When you are done with them, consider some of the brands mentioned here. Also check out the accessory forum. Plenty of info about screen protectors. Screen protect should not only protect the screen surface but also give you a decent writing surface. I used Fellow's screen protect way back in my Visor day. Well, let's just say one needs to start with a reference point

.
I use Pocket PC Techs' WriteShield C2. If it lasts as long as the previous WriteShield I had, I don't expect to replace it for another 12 months, minimum.