Might I point out that on a black Leica, the ribbed design will look far less obtrusive when the brass shown in the drawing is painted black like the camera? I don't know how the ribs would look with a chrome body where the vulcanite shows through the ribs, but for black, it ought to blend in well.
Grips are a very personal thing. Some people will like one kind, some will like others. Depends on the size of your hands, what lenses you use, your aesthetic sense, and occasionally, the phase of the moon.
To me, the (film) RapidGrip looks and feels big on an M. But it is very comfortable and stable, especially for someone with large hands. It's really good with heavy lenses like the Noct, 90/2 Summicrons, 75/1.4 Summilux.
The Leica grip for film M's matches smaller lenses better, but is less comfortable than Tom's.
--Peter