They look the part, but at the same time they are just a hole in the roof, the spinning around does nothing in the way of removing hot air - it's simple physics of "hot air rises" - the only benefit seems to be they keep the rain out. You could achieve then result with a pipe protruding thru' the roof with hood over the top to exclude rain.
To reduce heat in the roof space and its transmission into and thru' the ceiling is a reflective barrier under the roofing material and insulation on upper side of the ceiling.