Jess:

Any prop has to turn, obviously. And the less disturbed the air it turns through, the more efficient it can be.

When you have only a single blade there is no air disturbance from the other blade to go through, so efficiency goes up.

And this is why, generally speaking, a two blade prop is "Better" than a three blade, and it naturally follows that a three blade is "Better" than a four blade, and so on.

Three and four blade props are used on full scale planes to limit prop diameter mainly, but also for noise supression.

The disadvantage of a single blade, other than the counterweight, is the offset thrust load on the crankshaft.

Bill.