M performs and Akra mufflers are priced around the same. It's the old titanium v Inconel argument.
There's a you tube vid showing a before and after, stock and m perform... There's a 2 bhp increase but a 16kg weight loss.
I didn't get the pipes for performance and besides, I have a 2 year manufacturers warranty from BMW on the pipes.
This system separates the tame m3s from the wilder ones ( in the sound category)