YouTube has some videos where sellers demonstrate this kind of grinder, also the sharpening of helical milling cutters, grinding of lathe tools and sharpening of drills. Personally I like this one:
https://youtu.be/UEaTnSlPElE
If you are interested in the "grinding D bits" part, check out the channels of the tool and die guy and Stephan Gotteswinter. The latter uses a Chinese copy like the one the OP asks about and is very fond of it.
I have recently bought a used one (complete set with 5c collets) but haven't had much experience with it yet, so no opinion on how good the various attachments work.
Peter

P.s. Stephan also demonstrates how to sharpen the ends of ordinary milling cutters on his grinder.