As said before, Brabus shocks apparently aren't as good as standard shocks, it's only what I have heard from BIG Performance. They have been removing the Brabus shocks and replacing them with standard ones and geting better handling from them.
Brabus suspension only drops the car by 1cm, that isn't worth the effort.
The exhaust is a Brabus branded piece of crap, always have been.
They use poor quality stainless that rusts in no time, the tips tarnish badly and they barely increase performance at all.
This will probably be no better than standard with the strange USA exhaust setup reducing the power in the first place.
I've said it before and i'll say it again. Anyone who buys a USA Brabus needs their head examining.
You are better off getting a normal smart and modifying it.