I think the reason why we don't see more one bladers is due to the complexity of building one that runs balanced. Unlike a two blader, you have to balance the two sides of a one blader so that the center of mass on each side is equal. Other wise, the vibrations get worse at higher RPMs. If the c. of mass is further out on one side, the prop will want to wobble and vibrate. There is also the assymetric force of lift that the one blade produces and is not evened out by "another" blade. This probably isn't too much of a problem if you have a beefy enough prop shaft to handle the loads but it does wear the bearings a lot more. I have built a couple one bladers for S-400 pylon planes that worked pretty good. I have also seen some used for faster pylon planes. If there was an easy way of making them balanced out of the mold, I wouldn't mind building some more for testing.