I still don't undertsand why people still use external mods, Last week on Top Gear (UK) they featured an SL500 Brabus with over 650hp, when it came to handling the car was all over the place. Before a manufacturer releases a car, it goes through vigorous tests based on the power and chassis. If you add more power that has not been tested on the chassis, your car will end up a complete mess.
I've never liked anything that does not come from the manufacturer it always ends up useless