The gray (medium) stones chip with maddening ease. Both mine have one corner that I have to avoid. It doesn't matter to me anymore, as I don't use the corner now, but still, they chip easily.
The biggest issue with the Sharpmaker is it cuts slowly compared to coarse stones. If you have any sort of real damage to fix, change bevel angles, or sharpen a very dull blade, it can be very frustrating. My advice is to get a coarse, cheap bench stone and grind the edge down to below the desired angle for the Sharpmaker. Then, before actually forming an apex on the edge, start with the corners of the brown medium rods and progress through. This prevents the coarse stone from putting any deep scratches in the actual cutting apex. That would require even more metal be removed.
thank you!