I've spent weeks doing research and decided to start off with the smallest and easiest (reversible) change. I've seen myself how M cars easily lose performance when the exhausts are tinkered with so being very skeptical with this myself.
Here is a couple posts from other sites, its virtually identical to this.
OEM
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*Edit
To add
The entire rest of the exhaust remains OEM. I strongly advise against changing anything else on the exhaust unless you take it to professionals that really know what they are doing.
The primary and secondary cats keep the rasp away. The small resonator also keeps the crackling at bay. The X-pipe is well designed and positioned and gives good mid range torque and top end power.
The downside is the car is quite obnoxious when starting from cold. A deep and loud drone at idle. Quickly goes away once everything is warmed up.
I am very very happy with this result and will not pursue any other change or sound
