I'll add something here in reference to multibladed systems vs. 2-blade, teetering systems. (Keep in mind I am discussing only findings derived by lots of experimentation on MODEL autogyros.) Also, the following is NOT comparing net lift, but ease of control; roll-pitch stability:

A multibladed rotor system, using individually flapping blades and not too light a disk loading, is noticeably more stable throughout the model flight envelope. Particularly on gusty days, the multibladed system is much less "bothered" by bumps and breezes. Without pilot input it seems to compensate for these irritations. With normal pilot input, the gyro just flies so much smoother.

My one reservation is on VERY LIGHT disc loaded, multibladed designs: fast rotor rpm ALSO promotes stability. A multibladed system in full autorotation turns slower than a 2-bladed system of the same dimension and weight. Since very lightly disc loaded model rotor systems rotate more slowly, you may not notice the stability improvement. Load the system a little, though and you will.