My main criticism for the mircocell pad is that after they are ground to fit the sides are very grabby. I don't like that aspect at all. I have a couple old ones around here and I'm going to experiment with some sort of coating to make the sides slick.
Yes they are more finicky to work than hard rubber pads.
Grinding Instructions state: "For best results, it is necessary to use a high speed machine with a 400 grit sanding belt. Use a new and lubricated belt and pad should be gently drawn close to the belt."
When trying to get a local gunsmith put a pad on for me he stated he was only set-up for 80 grit only and did not want the work of changing over to 400 grit. I found with 400 grit it was not hard to properly shape.