not that im a tech, but from what i understand when the Diverter re-routes the air into the intake for the fraction of a second that it does, all that it accomplishes is relieves some of the vacuum pressure the engine is putting on the intake for that fraction of a second. Then the engine goes back to working as hard as it has been through the rev range to intake air.
So, correct me if im wrong, but by re-routing to atmosphere all we are doing here is not giving the engine/intake a little boost/break from vacuum pressure for a fraction of a second. I doubt this greatly hinders performance on a 300hp TT car.
So its noise vs. a very small fraction of a second faster (if anything)