I was reading a Wikipedia article on sharpening stones (looking for a replacement trapezoid shaped jeweler's stone that I used for serrated edges, which, unfortunately, I broke), and it mentions that Belgian Coticule has been prized since Roman times for the quality of edge it can put on a knife. I like natural stones, but am used to hard Arkansas. It says its equivalent to 4000 grit, which makes it extra fine.
Is it really worth the $25 for a small (3 7/8 by 1 1/2 stone)? The Case Hard Arkansas I frequently use is just under that size, but cost $8.