Not to be a party crasher but it is from the experience spending enough money to buy a 911Turbo on unnecessary gears and hopefully second thought people who itch to spend money on these accessories. Everything changes sound to some extent when you stick it into the system. Ask yourself first what is it specifically you are looking to gain in your system. Is that thing lacking in your system. If your answer is yes then pursue to find a solution that might fulfill that goal. Don't just add something to increase something when you already have enough of that in your system. Footers will alter your sound some way. If you pay a very high price for it and have heard comments from others that it is good, you likely will accept the sound as improvement when it could actually be excessive. Very expensive accessories are not worth buying imo. Better put you time and resource in finding gear that is excellent without adding. But if it is something like you want to buy new wheels for your Ferrari, then it is fun to spend money on these things. The M3 is already excellent by itself imo.
sincerely,
Tang