Quoted from VolunteerPin:A little off topic, but mentioning the scratched glass makes me wonder if the Invisiglass scratches and easier or less often than normal glass. I've thought about buying a couple of sheets but have to bring myself to do it.
Yes, it will scratch more easily than regular glass, as it's coated. See this thread:
http://pinside.com/pinball/forum/topic/jersey-jack-invisiglass-has-a-scratch-in-it
In general you get best optical properties from glass that's coated for the application required, but the coatings are generally more delicate than a hunk of glass is. (I work in a laser lab.)