...my first CBN wheels took a long time to come up to speed, even with a hand push to get them started. Then I got a Baldor. I did pick up a 1 hp Rikon years ago, one of the first ones they were putting out. I had to grind about 1/8 inch off of one leg/foot to get it to sit level on some plywood. I picked up a second one a year or three later. I didn't have to grind anything off of the base to get it to sit flat. They and the Baldor grinders come up to speed in the same amount of time. The Rikon spins for a loooong time before the wheel comes to a stop. The Baldor comes to a much quicker stop. I still still will use the heel of what ever tool I am sharpening to stop the wheel on all of my grinders. The 1/2 hp Rikon just doesn't have enough horses for me, though they do work for many turners.
Some have reported with the extra weight (mass) steel CBN wheels don't spin up well on the smaller bench grinders. I used aluminum CBN on a 1/2hp Rikon for a long time and it worked well.
Nearly all of the bench grinders I have (except for a Metabo in my little weld shop) needed some foot leveling for the cast iron body to sit flat.
I've had a couple of grinders with internal electrical brakes - I'd hear a click when a centrifugal switch caused the break windings to kick in to slow it down. As you imply, stopping those that freewheel is more of a problem! I use a stick of cherry, maybe 1.5" wide, 3/8" thick, and 8" long to stop the wheels - just push the angled end into the side of the wheel and the friction slows the wheel down quickly. (Silently spinning wheels are a hazard, especially around klutzes like me!)
JKJ