Interesting Roof Vents

Interesting roof vents on a ~$1M, 1997 built house today. They rotate in the wind and appear to function by venturi effect. The house had three of these and two box vents - very unusual. When I first saw one from the attic below, it looked like an abandoned flue vent in the roof.

They must be stealth vents - note the low radar profile with the angled trailing surfaces :mrgreen:

Anyone know who makes/made them and whether they are effective?

Pretty cool vents! No problem.