I too knicked mine up the first time. And I too was recommended a piece of pumice and it worked very well. Also, I found a superfine grit metal nail file to work wonders as well. I also used some Dovo leather conditioner over the cuts immediately after sanding them to hydrate the leather a bit.

You may knick a strop the first few times you strop but eventually you will get the motion down.

I now use my first strop as a travel strop and haven't managed to knick my Tony Miller.
Good luck!

-Kyle-