These things are great for polishing polymer.
I use 80. 220, and 320 grit in 1/8. 1/4, and 1/2 size.
They work for removing the parting lines on your frame before using a polishing wheel, then soft brush with polish to bring back the luster of the frame.
When a shape a trigger guard with a sanding wheel I go over with these to knock off the edges.
If you want to round off some sharp edges on a frame these work great and then polish luster back.
You can shape these by running the on a cinder block or very course stone. You can clean them with the same stone when they load up. Just remember to keep them moving so they don't build up heat and melt polymer.
I know they are expensive, but they last long.