Sound wise Hamann/Supersprint are ok. Not too loud for me but I'm scared it might be too loud for my wife and kid.
Performance wise, there is a gain in the upper range but a slight loss in the lower range. Since I rarely go over 3K RPM, not very useful for me.
For me, it's solely for the looks. It just totally changes the rear of the car. Pretty much what the m-sport bumper will do to the front of your car.
That's why I was in a predicament. Wanted the looks but wanted none of the sound and loss of low end torque. Finally Z shop found a way.
