I use plexi OP-3. The problem I initially had was scratching it when initially cleaned it after removing that damn paper.
I was laying the metal frames on a towel when assembling them and some minute iron filing (aluminum filings) would get somehow spread around and when I used a towel to clean off the plexi cleaner, I'd scratch it.
So now I'm anal. I assembly the frames with care not near anything that will come in contact with the plexi. Then I use special plexi cloths (blue face cloth size fine terry cloth looking things) with Brillianize plexi cleaner. I wash all the cloths and towels after each session. I haven't had a scratch since.