Drang, the advantage here over the Savonious is that the fan is the generator.
I got that, and it can be a very big advantage.
The Savonious still has to turn an alternator, and is far less efficient. At least that's the way I understand it.
One big advantage of a Savonius wind turbine is that it will start generating at very low wind speeds; unlike the Darius style vertical axis windmill, it should not need to be "push started" at very low speeds. It will, however, "max out" at a lower speed than other designs.
Another disadvantage is that they are very tall, and cannot be roof-mounted.
If factory-manufactured (i.e., not out of split 55 gal. drums) they are practically silent. I suggested to a factory rep that he should try selling them to HOAs as "kinetic sculpture with benefits", since HOAs are usually as fond of wind generators as they are of amateur radio antennae...
There are trade-offs with all these designs. Efficiency v cost v cost-effectiveness v footprint/size-and-space consideration v maintenance v ...