ORIGINAL: LancelowDowell
I remember seeing one of the carbon fiber prop makers sells props for rc with those tips on it... can't remember who made them though...
http://tntlandinggear.com/store/shop...e_aircraft.htm
These particular props probably do not increase efficiency much (if any), and they certainly do not reduce noise levels, but they do add noticable stability in hovering-type maneuvers. This is due to increased prop normal force, according to an aero engineer whom I asked about it. I know I felt a HUGE increase in high alpha/hovering stability when I switched to a Prince prop for 3D.