They think the design has advantages over single static windmills:
Like a flock of geese, each rotor favorably affects the next in line. Like a set of louvres, the tilted rotors pull in fresh wind from above, deflecting their wakes downward to insure fresh wind for succeeding rotors and, like a stack of kites, to add overall lift which helps support the driveshaft against gravity and downwind thrust forces. The rotors act as gyroscopes or spinning tops, stabilizing the driveshaft where they are attached.
No prototypes made so far.