There is only so many ways to skin a cat. Very happy with my Megan exhaust and I've had experience with many exhausts in my ownership of 2 E46 M3s to a 07 997S to include, Borla, Supersprint, AWE, Fapspeed as well as Eisenmann.
You guys want to spend the big bucks out there for an exhaust to say you got "brand X", knock yourselfs out. I for one don't feel there is much difference that you will see. The Megan is actually a pretty good exhaust and the fact it copied the Agency Power exhaust doesn't bother me one bit. Who the hell looks under the car and "oohs an ahhs", he's got a Akrapovic...or a Eisenmann or insert any other brand."
This you got an "M3" so it deserves more...LOL, its a car, a nice one but still a car.
2013 M3 Coupe-MR/BLK ZCP, identical to my 2011.
2011 M3 Coupe-MR/Blk
2007 Porsche 997C2S Speed Yellow/Blk sport seats
2004 BMW M3 Imola/Blk