One fact is, your insurance company will "rob" you for fitting that! I bought a secondhand S4 and its original owner had fitted a Milltek exhaust, which I correctly informed my insurer about, I think that it currently costs me in the order of £100 a year for that, trouble is, I could probably fit a few more mods without paying any more, but I'm not brave enough to ask that question as they might sneak in another few hundred pounds next year.
When I looked into changing to Audi insurance, it all looked good until I read the small print - ie "fancy bits fitted - go away!".