I've been told they are great for of the mark excelleration as in Drag racing but shithouse in city traffic.

                                                                                                                                                                                           Ductor

Jeez, I thought someone exposed himself at a primary school. 

I like the look and the sound, but have no idea the pro's and con's

i have one on my 84 softy chopper , it's a BDL 3 inch unit and have had no mechanical problems with it at all .
yes it is a little noisy with the clutch pulled but once engaged no noise at all other than the whine of the air getting caught between the belt and the pulleys.
does tend to chew the rear of your shoes if you forget where to put them on the pegs, toes out helps.
and i guess the most important factor is that an open primary is illegal in most states if not all, so i run the gauntlett every time i take her out .