VAWTS (e.g Quiet Revolution) are normally better performers in built up areas as they can catch the wind from any angle in turbulent flow. The Energy Tower appears to be uni-directional so presumable has some automatic luffing mechanism to allow it to face the wind, in which case turbulent windflow isn't helpful.
The blade construction and driveshaft look pretty spindly so I'm guessing this is a relatively low output device.
Questions - how do they prevent overvoltage on they output? I guess they can throttle the air escape to give a maximum rotation speed?