I think the 254mm diameter is a tad too big/fast for a standard bench grinder. When I first got them and mounted them on my grinder, I quickly moved it across to my lathe.
I always kept my eye out for a slow/variable speed grinder and as soon as I found one I immediately bought it... this was actually for my buffer (which I bought first) but was repeated for the flap wheels.
The 1/2 speed (1400RPM) is acceptable for most sanding jobs, however, if I need slower or more delicate work, I temporarily move it across to the lathe.
The buffers are mounted on a 1450RPM grinder (and another triple set on my variable speed mini lathe).
If your first cut is too short... Take the second cut from the longer end... LBD