The GRS vs Lindsay airgraver is an endless debate. Both are proven systems. In a perfect world, demo both. I will add a note about the statement of the GRS having a larger power range. That might have been true at one time, but with the option of a tungsten piston for the smaller handpick and the advent of the Nitro hand piece, the Lindsay has the larger power range. One of my students bought one of the new pulse airless gravers from Tira Michell is very pleased. It seems to be priced more modestly than the GRS or Lindsay.
On the subject of make you own power graver. I know a guy who tried making his own and threw it away after wasting a lot of time. Getting a power graver to start and stop in a predictable manner is critical. Both GRS and Lindsay have been designing and machining these for four decades, so they have a pretty good handle non making a good product.