Well i've only completed 2 grooves, so i would not take much grooving advice from me but here's my setup.
I use a Rotozip RZ1 with a flex shaft. (5amp/600W/0.8 HP)
Pros: Flex shaft, Massibe Power to cut or grind anything.
Cons: Single Speed spins at 30,000 RPM which is about 2X what Ron just told us we should be spinning at to extend our bit life,
Possible Mod: I may try an old sewing machine pedal to create a variable speed grinder. Not sure what effect this will have on the motor over time.
I hold TB in a vise so I can concentrate on proper angle of my bit. Not sure how Ron holds the TB in one hand and the grinder in the other and get good grooves. Lots and Lots of experience I guess
Other Grinder motors like the jewelers flex shaft type are about 1.7amps/204 watts/.27 Hp. Quite a bit less than my grinder. Obviously they are sufficient as this type is what Ron and Michael are using I believe.