I bought a Prodigy Flex Shaft a few years ago before I started making jewelry. I didn't want to buy a new flex shaft to put the stones in my bezels, so I hoped that would work. and so it is. I have a speed controller and I set it to 15 percent. The Prodigy can operate at 20,000 RPM and this handpiece cannot be used at speeds greater than 5,000 RPM. It works really well at around 15 percent power.