I have two disc grinders in the finish shop....and one in the hot shop.
The two in the finish shop are both variable speed, one is the 1hp/VFD from Beaumont (KMG), and the other is a Dayton 90VDC 1HP & DC speed controller. The key to both is the discs used, or more correctly the disc systems....
https://www.facebook.com/NielsenDesignDiscGrinders/
I simply couldn't use a disc grinder without it. It's an arbor/hub that holds face plates magnetically. What's so nice about it is that you can get both flat and 1 degree tapered disc faces. The 1 degree tapered disc faces are just awesome! They allow for grinding past the center of rotation, without the other side of the disc trying to grab/throw upward whatever you're grinding on.
I have several of the disc faces, which means I can keep various grits, on the faces, ready to go....and change them in just a few seconds. It also saves a lot of sandpaper in that I don't have to tear off/replace a barely used paper, when I need another grit, as would be necessary with single disc/face.
Here's the Beaumont/KMG:
And the Dayton/DC (you can see rack with the extra disc faces standing by)
I normally don't have the table on this one..... but every now and then the table does come in handy.