
Is the sensor cover plastic or glass? And how easy does it actually scratch?

It's glass
yes - it's glass, although having said that there are coatings on the surface and it's really these coatings that are damageable so you can't quite treat it like you would your car windows & give them a good scrub up. Having tried, I can say a fingernail can scratch the coating but you'd have to be trying quite hard!