Variable speed is always useful I think, and 8 inch is probably better for a flatter surface to grind against. I actually find the vertical belt sander to be much more usful than the grinder. It's a wider surface, maybe an inch and a half with a long vertical support behind the belt to easier shape whatever I was grinding.
I agree, a vertical belt/disc sander is much more useful and much more cost effective. there are inexpensive bench grinders out there, but they are poorly made and most times do not have a true spindle which makes the machine vibrate. a good bench grinder will run so smooth that you won't know it is running, and those cost three hundred and up. then there is the task of truing the stone and the tool and skill to do that. with the belt/ disc sander you just change the abrasive. you will be able to accomplish many more tasks than a grinder.
