Fitment is better with exhaust welded rather than clamped, no risk of it coming apart (they do over time) and all clamped pipes will leak at some point.
That being said, clamping is fine, welding is better, albeit more permanent.
That flap in the exhaust of the 330 is a loud thing more than anything. The E46 guys usually mod the flap to keep it open to get more sound. Torque isnt affected.
A 330 owner would upgrade for sound and looks.