According to my old aeronautics professor, 2-blade turbines are the most efficient when pointed directly into the wind. They've tested 3-blade, 5-blade, and vertical turbines and couldn't get the same amount of output. These experimental turbines look great on paper but rarely scale up.
The reason why 3-blade is the most common design is 2-blade turbines induce a lot of harmonics at high speed. 3-blade cancels it out but are slightly noisier from the blades slicing through the spoiled air.
Actually it is the opposite [1]. Efficiency is theoretically increased with more blades. The three-bladed turbine is the most popular because of the cost benefit of building blades vs efficiency gain of extra blades - although the case of harmonics for even number of blades does hold true.
If I read various parts of their website correctly it sounds like they aren't in the turbine business(yet), but building this funnel thing around many existing turbines.
The reason why 3-blade is the most common design is 2-blade turbines induce a lot of harmonics at high speed. 3-blade cancels it out but are slightly noisier from the blades slicing through the spoiled air.