Green light for McLaren's controversial wing

I don't know or care much about F1 these days but I thought that ito aerodynamics the car had to be "fixed" i.e. no mechanical moving bits. Oh well, good luck to McLaren, I hope their trick works. Silly to have a magic hat with no rabbit in it. It looks like a simple way to reduce the negative pressure behind the wing i.e. reduce drag. I wonder what will happen it the valve gets stuck open at the end of the straight and the driver has reduced rear down-force... Sounds a bit dangerous to me. Hit the switch mid corner and a swift exit in reverse may add entertainment for those waiting to see a crash.