I'm with you - I think it's a great look and adds a little character to a bagger.
I previously installed a 2-inch DBL on my '05 Fat Boy which allowed me to keep everything where it was (floorboards, etc.). A new belt drive will come with a motor plate that takes the place of your inner primary. I also have a 3: DBL on my custom chopper - will chew on your shoes just a bit sometimes
From my experience and some of those around the Indy shop where I frequent:
Pros:
Appearance,
sound (unmistakable sound like a blower almost),
no more primary fluids,
no more primary chain adjustment issues,
elimination of troublesome compensator sprocket,
feels more responsive to throttle,
some claim gained HP due to reduction in rotating mass
Cons:
Sound (some don't like it - you'll get more pronounced clutch basket rattle, etc.),
no compensator - even though these have been troublesome they do smooth out the transitions from standstill to a slow roll,
watch your gear ratios - depending on the product you purchase, it MAY cause a change in your overall gear ratios (in my case it made my gearing too tall for the Fat Boy)
Do your research and it can definitely be a good thing! Good luck with the project - and by the way, this is typically NOT a difficult change.