Hi,
i know its boring but if you fit an after market whooshy dump valve you run the risk of letting small amounts of unfiltered air into the induction system just before you put your foot back on the throttle, the standard dump valve is a much better option and you don't sound like every other chav on the streets either?
Apart from this, German engineering is the best in the world and a £20.00 ally valve is not going to make it any better, if it did then it would already be on the car from the factory?, why dont you spend your money on some big brakes or decent suspension or just go down the pub......unless of course you are seventeen and wear Burberry, then you may as well buy the valve and go on a cruise!!!!