I have a watch with a plastic crystal that gets chips often.  I guess i'm rough with my watches.  This Polywatch product works great!  I dab a little on a old cotton cloth and start rubbing away.  I find it works best if you work in a fast repeated linear motion over the scratch so that it gets very hot.  Circular motion took longer, you need to get the heat high.  Careful though, i burned my thumb once.