Car will sound like (more like) a WRC car.
You DO loose the beat of the boxer but you DO gain torque from them.
If it was me I would buy them *price depending
I run semis and have lost a little of the burble but its worth it if your serious about the power gains
Cant give you figures on mine as it had a flywheel, injectors, pump etc fitted and also mapped afer having them fitted.