Full Muzzy systems rock!!
on a side note, it's a parallel twin. It will always be a parallel twin. No matter what you do with the exhaust, nothing is going to change the fact that the engine is a parallel twin and sounds like a lawn mower when under 5k.
Also, intake noise sounds way throatier than constant exhaust farting, especially if you're just going for throatier sound and not a loud bike. I suggest
modding the intake lid or ditching the airbox for a K&N pod filter if that is the route you would like to take. Both are much less annoying than an exhaust while cruising, but sound better when you tap into the throttle and load the engine.
Slipons for this bike are all really loud and don't do much. A Muzzy makes a difference in performance, but is definitely louder than stock without being nearly as obnoxious as the slipons. The muzzy sounds fantastic though; very throaty and low at idle, but still rips up top. If you can afford the Muzzy and a rejet, go for it; I like mine a lot.