I have the exact Supersprint exhaust as the one in your link on my 323i. It's perfect for me, the sound is moderate when in low revs but picks up nicely in higher revs which i what i wanted. It's not stupidly loud like i've heard some of the scorpion ones to be. It also allows the raspy sound of the 6 cylinder to still be heard.
Was easy to fit also.
Perofrmance wise i couldn't say as i haven't dyno'd it, feels a bit more responsive though overall, especially in the higher rev range.