Just about anybody could build one of these by cutting steel or PVC tubes at the right angles.
Throttling is just as important as low wind power because in order to reduce maintenance you don't want storms tearing it down every time you get a 300 mph wind up there.
I have not got around to it yet on my list of projects but building a housing for one of these has been on my TO-DO list for years. A cage designed to keep people from vandalising it topside. Will be building at least one of these to go on the roof for testing in 2017.