I just installed the GRP Titanium Exhaust for 2.0 Turbo AMG (i4) where I reside in Tokyo. I also installed the Milltek Type 2 valve controller. The loudness in OE mode is comparable to stock exhaust, but ‘tone’ is improved. BTW: I have also performed DIY “fake sound delete (cut) inside the car, so no more fake sounds from KEF stereo/subwoofer. A big relief!
Moving the Milltek valve to “open” gives a considerable boost. However my main concern is to have my installer run the car through the official test and get official approval for the OE sound level with a certificate on paper and a titanium plate with stamped / punched letters / numbers representing the approval registration will be attached to the exhaust surface.
In addition to the improvement of the external sound, I can also confirm that the internal sound (after the delete /cut of fake sound through the stereo) by the GRP Titanium Exhaust for 2.0 Turbo AMG (i4) is also noticeable and positive, without being excessive. (Notice that I have not altered or removed any emission related equipment on my car, because it is my intent to keep the car legally compliant.)