I’ve been thinking about getting a coarser water stone (or diamond plate) for a while, to make shorter work of thinning and sharpening damaged blades. The other (full size) stones I have are the #1000 and #5000 Naniwa chosera and a #13k Sigma Power that I bought last year. The one I use the most is the 1k chosera.
The reason I went for Sigma Power is that I wanted something fast cutting, but less delicate than the chosera stones. The chosera stones are great, but they’re kind of picky about how much water you use, how fast they dry, temperature changes, etc. No matter how careful I’ve been, they’ve developed many small and a few deeper cracks that make me kind of nervous. I had read about people testing Sigmas by putting them in the freezer and defrosting them without any problems. I don’t feel worried at all using the Sigmas. I looked at other stones as well, like Imanishi/Bester, but they seemed to have the same drawbacks as the choseras and pretty much no advantages.