This is indeed an improvement over a tetrahedral pin.
This reminds me of an Exact Constraint coupling between two bodies which consists of three V-shaped channels that accept three spheres. Since the three spheres make contact with six planes, that constrains exactly six DOF. If you delete one of the four features and reposition the three remaining features at 120 degrees around the circle, that is what I am thinking of.
However, the other end of the shaft constrains 2 DOF so that connection is over-constrained.