i think the bmw ones arent functional in the slightest.
Its a common thing done by drifters in oz and nz and it does make a difference.
as for decapitation.....erm nope, its exactly the same as being mounted normally.
as for not being allowed at santa pod, well ive seen people run with the bonnet up like that.
BUT
not much needed on this car even in the carribean, unless its running a bit hotter than normal due to tuning stress'
there you go my 2 pence worth