i have rubbed a fair few opals with a bench grinder for an initial shape and "rough" polished all with a circular sandpaper, the velcro backed one for padding. And as fine a grit as i can get 1200 or so, attached to the side of the new stone with no issues at all. For practice stones and roughies its great and very affordable. For the water i use a trough (plastic 3lt milk bottle cut at the bottom to keep the water flying everywhere, and a squirty bottle of water to keep the wheel wet. i dont run a guard. The water stops the stone getting hot and cracking more than any dust issues. it isnt in the same ballpark as the 12000 grit Diamond laps at the lapidary club for that final polish and gleam and i recommend anyone interested in cutting go at least once. Its awesome fun. The above is for rough material i dont care too much about, or have less than 1% chance of cutting a gem. Its practice material. Not gemmy.
I also agree, in the name of safety. having a belt drive the other wheel would be v advantageous.