Interesting rudder shape

I've never seen one of these. Seems like it would increase drag. Thoughts? Is it a really good design or sold by a really good salesman?

 

Lot of the early to mid 80s Bristol Bay boats had the split wedge style rudders. Think our first power skiff had one originally as well, was told it was done to keep the rudder from pulsing in the natural slop of old mechanical systems. But I've heard reasons ranging from it helping turn in deep tunnels to helping reverse maneuvering.

 

They were an attempt to minimize the tendency of "prop walk", in order to provide a neutral helm.
Kind of a fixed trim tab, if you will.

 

Thanks!