Their big advantage is that they do not need to be pointed into the wind, and appear conceptually simple, they also have their generator on the ground which is an advantage. But they suffer from oscillation and vibration and such low TSR designs as the one in the article will suffer from shading. The concept can work, but typically the machines end up requiring a lot of maintenance and extremely careful design.

The biggest of these, the Cap Chat Aeole ran for an embarrassingly short time before destroying its main bearing.

http://www.wind-works.org/cms/index.php?id=506

It was a most impressive machine though.

A more successful project was run in the Rocky Mountains where a number of such Darrieus rotors were in operation for quite a while. Even so, the concept is problematic and will likely never see widespread use, even though you'll see a flare up every couple of years when people new to the matter think they have found gold.