I have something similar somewhere. Which might tell you how useful I found them

Foredom do an extremely fancy version called the Allset. Never used it, although I did once consider buying one. They're great in theory, but unless you're working with calibrated stones all of identical cuts you'll probably spend more time mucking about with the tool than getting the stone in. And even then I'd worry about how much extra space is needed around the stone to give clearance for the tool.