For the concrete performance numbers, see Post #776 and #777. They back up the Betz Limit claims and more so.
The numbers are from real-world testing on a 1 kW WindTamer. Mounted at a hub height of only 13 feet, and it broke Betz Limit. Independent testing by wind-power authority (see Post #775) Dr. Ken Visser of Clarkson University.
I agree with you -- I wish they WOULD start singing from the rooftops. Maybe they don't dare until they have the necessary manufacturing capacity.