BTW - I can say w/ absolute certainty that DINAN has had at least a test version on a 1M in May at Bimmerfest. Because I took a couple pics.
http://www.enthuzeus.com/photo/QqTyj6a
http://www.enthuzeus.com/photo/QqxB5uF
I heard it briefly - but didn't get my phone out in time for a vid clip
Defn was louder and deeper than stock, but not obnoxious. No idea as compared to other aftermarket exhausts...