I know several here have used them, so I checked out the web site. The site says the usable abrasive is about 5mm thick. I am assuming that they are a version of waterstones, which wear pretty quick IME. Do these stones wear out quickly? How is the cutting speed vs. achieved finish in the coarser grits? I'd like a really coarse stone to use before my 800 grit waterstone, without spending more than about $40, and the Shaptons look promising.