Since the blackstone silicon grindstone (SB 250) has the same grit as the SG 250 original stone but grinds HSS tools faster and also touches up tungsten carbide, why would I want to use the original SG 250 grindstone? If there is a reason, you should at least explain that in your "Grindstone" page on this web site.
While the SB stone cuts HSS faster than the SG, it does not cut normal tool steel as quickly or efficiently as the SG. While the engineers disagree with me, I personally don't feel the grader is quite as effective on the SB stone, either. I can't get as fine a finish on tool steel with a graded SB stone as I can with a graded SG stone.