O'Hagin vents for exhaust

We are getting a new roof in two weeks and the roofer wants to use O’Hagins for exhaust. He used to use turtle vents, but said that the O’Hagins work better. With these low profile vents, does the hot air have to travel down out of the vent as with a ridge vent? Or is the air allowed to rise completely and just pass out of the O’Hagin vent? The reason I didn’t want ridge vent was that I have been told that they don’t work well. Thanks.

I’ve used them quite alot on tile roofs but never on a shingle roof.

Assuming you have a shingle roof then a ridgevent would be the best way to go when accompanied with adequate intake via soffit vents.