I've been using a four surfaced emery board that has two very fine surfaces, one blue and one white. After getting the surface down past any deep scratches with the blue I polish it up with the white, then finish up with PlastX head light lens cover polish on a cloth. results have been excellent.
Hand work only. I see no reason to use any power tool on a watch crystal.
PS
Its best not to go over board in trying to polish out very deep scratches. Any remaining mark will be rounded out at the edges enough not to be noticeable at normal distances.

 

I have a feeling that Novus 2 may be slightly coarser than PolyWatch. But I couldn't say that one works better than the other, since coarse and fine both have their uses. I haven't tried the finest Novus.