The sprag is not a new idea in aircraft soft-start and free-wheel clutches.  Pretty much every helicopter flying today uses them so that in the event of an engine-out, the pilot can auto-rotate the helicopter to a safe landing, in much the same way a that gyrocopter always operates.  Arrow, and Italian 2-cycle engine builder, started using them in their gearboxes to soft start their  engines in 1980.  They found their way onto many gyrocopters, and in 2012 MAC started using them for Yamaha YG4 engines converted to aircraft use.   GT5 is assembled with a clutch element which has an integral ball bearing set, thus the complete clutch can be made much smaller and has no need for additional bearings or grease seals since the clutch-bearing element has its own rubber lip seals.  The result is a very narrow, lightweight clutch that can be a direct swap out for the RK400 and weighs less than half of it.  

GT5 Sprag Clutch