I removed it and have no regrets. I loved it with OEM exhaust but when I switched to Akra Evo the cold start was obnoxious. It had a low resonance that was not pleasing. Some other exhaust systems may have different results.
'04 E46 M3 - Jet Black - Sold
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'13 E92 M3 - Alpine White - 1 Option (DCT), Ohlins TTX, AP Racing, Cobra Seats, Akrapovic GT4, BBS E88, Volk TE37, M3 GTS - Steering Wheel, Aero, 1/2 Cage, Seat Delete