CBN grinder wheels

A waste of money. Spend your money on a grinding wheel dresser instead Keeps the wheel flat, square and cleans the rubbish off the surface. Example:-

They seem very popular with wood turners and carvers who need to sharpen lots of HSS tools. They have an advantage they can run quite fast and not burn the tool - so you can get away with sharpening on normal bench grinders, and not just the geared down or water bath grinders.

Price is relative - they are cheaper than buying a Tormek system (although their jigs are pretty nifty for some tool types)

Somewhere along the years, I have picked up the idea that silicon carbide (green wheels) are best for cutting tools.

The cbn OR diamond wheels are great for carbide tools.

Diamond is usually preferred for carbide, but CBN is better for HSS tool steels since it grinds fast with little clogging and the grain structure is not broken by the steel - so you get very low wear rates on the abrasive. Hence no need for dressing.

Green wheels are really only necessary for sharpening tungsten carbide tools. I have a larger than average diameter regular wheel for rough shaping and then fine shaping and honing with a linisher. You can't beat a flat surface for tool sharpening.

Clearly harry your definition of 'flat' and 'square' isn't