I did some checking on Grainger’s sight. Both buffer/polishers and grinders, that I looked, run either 3450 or 3600 RPM. The FPM would be determined by the size of the wheel and would become less as the wheel ( both polishing and grinding) became smaller. You want the speed to create heat when polishing soft metals. As the metal expands it brings the imperfections up to where you can buff them out, or reduce them, depending on how deep they are. After you strip all the stuff off a grinder, without the extended shaft, its really difficult to do large parts, like gear cases, or gas tanks. If you’re just polishing jewelry a $50.00 Harbor Freight grinder would be adequate IMO. My experience is only with an arbor, one grinder, and a $40.00 buffer. There are so many options that I have no experience with and know nothing about. I suspect that if you spend $500.00, $1000.00, $1500.00 or more for a polisher, it would likely perform better than and a $40.00 buffer, but its just my opinion as I only have experience with a $40.00 buffer. Tubs
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.