What's that "F vent" all about.? From what I can work out its a wee flap that deflects the air away from the spoiler on the straights thus creating less down force.?
Moving the driver's knee lets air through a snorkel on the top of the monocoque. This is channelled down the fin on the engine cover and dumped through a slot in the wing. This stalls the wing and reduces the drag thus increasing the straight line speed. McLaren have been clever, the FIA have given it the thumbs up and as there's no moving parts, it isn't classified as a moveable aero device.
The other teams have the arse because the tubs have to be homologated which means they can't be altered through the season, thus making it difficult for teams to copy McLaren's design