I bought a set of Splits with a black chrome jaw. Hated the look and posted in classifieds for some polished black ones. Nalong86 was nice enough to give me as set but it had some minor chew marks from a dog. I wet sanded it and hand polished it with the Plastix and it looks almost perfect. There's only one spot by the bolt which has noticeable marks but you would really have to look at it to see them.
I only used it on the polished black frames so if you are going to do it soon on the crystal ones, try it on a spot where it might not be noticeable. I'm set to buy a pair of crystal Gascans tomorrow and if I do get them I'll post up if the Plastix works on them too.
If anything buy it anyways if you have plastic headlights. My Tundra ones haze up fast and this thing makes it look almost new.
Couple more things. I'm not sure how the polish reacts to the paint or iridium coatings which Oakley uses so beware when using. Also, if you are thinking of making a matte frame into a polished one, beware. I had a old pair of "new" M Frames which came as matte and I thought it would look great polished. I used the polish on the arms and they made it real nice and shiny but when I tried to polish the center section it would not get as shiny as the arms. Seems like the plastic used for the center is different than the arms.