I use that all the time.
It's basically just a plastic sanding block with wet / dry automotive sandpaper.
I went to my local tool place, picked up the block for $3.00, and got an assorted
group of grits on the sandpaper starting from 150 and went up to 1500 grit.
Total cost me about $15.00

I've used it to strip the coating off of a couple of knives, and to put a
convex edge on a couple of knives.

Although the block is a bit too big to take with me in the bush, it is good
for around home. Bought a smaller sanding block for the bush. Works just
fine. Allows me to touch up my blade edges.

Cheers