Those are the figures that Judd themselves gave, but now the website says 800+bhp without air restrictors.
http://www.mulsannescorner.com/juddgv510.html
And with the fuel flow meters, the point is to lift and coast. They're there for the same reason air restrictors are, to limit the performance of the cars. If you're going to give them enough fuel so they don't have to lift and coast, then why run the flow meters? May as well go back to air restrictors if you're going to do that.