I am not using diamond stones - I have no idea where I got the stones I have, the double sided ones (course and fine) grit seems to be good. By that, I mean as I roll the KME, the film of oil on the stone I applied is evenly "removed" as the head goes across the stone.
But my smooth stone ... there are "gaps" ... streaks, like the head isn't sitting evenly on the stone.
If diamond stones are all that, if diamond stones would take my sharpening to the next level and my heads from popping hair to scalpel sharp .... I'd buy them