adelaide;
Well, I am very far from any kind of "expert" but my opinion on the 2 blader and any benefit it may have is they are completely and utterly offset by the fact that the yaw shudder will more than likely destroy the mill in gusty locations.
The blade root takes a helluva beating every time it does it as do the bearings, shaft, bolts and damned near every part on it. Not to mention the horrendous Noise.
Some folks find them to work OK but for me I will stick with 3 blades or more and always an odd number.
Just my experience and observation.
Cheers.
TomW