This is a good point.

Having even fewer reservations about putting plays on your game is a good thing. This is how I feel about Cliffys in the shooter lane. Get them in place and worry not in that instant when you press the Start button and hear the thunk of the ball eject.

Something more:

I've played certain collector pins on location with PF protectors and the ball can skid/glide far more easily than it can without the protector. This means the ball is moving but not rolling after it's flipped. That means the physics involved are a bit different when it strikes an object on the PF. Can you tell? Honestly, yes. The ball moves in a way that is slightly peculiar. Sure, a fresh coat of wax should theoretically produce the same effect - and in many cases it does - but that effect is temporary. Even a coat of Blitz will "tack up" after a couple of dozen plays.

The part about debris collecting under the protector and scratching the PF seems unrealistic. Unless your location is filthy, I don't see anything of consequence making its way under your protector. And even if it did, what friction would come into play that would grind the dirt into your PF? If the protector is properly in position, it will stay in position. They don't slide around. They have numerous indexing holes.