Yes there are certainly arguments against using them. They were fitted to my 135 when purchased 2nd hand, I'd not personally fit them myself.
Interesting thread here on the matter:
http://www.1addicts.com/forums/showthread.php?t=211966
The exhaust is certainly worth the money for a car that certainly sounds incredible! I am actually embarrassed a little in the mornings upon start-up - car resides in a garage which only amplifies the tone and it's quite something - fairly OTT! Also tends to be louder than I'd ideally like at below 3,000 RPM (highway cruising) but it's blowing a little at the flanges and might quieten down a little after present attention @ BMW service. But when out and about and giving it stick, it's out of this world... I had a Golf 5 GTI before which was timid in comparison!