i guess purpose boils down to personal taste... and arguing about that - you know that will go down the drain...
purpose of a rigid frame chopper with a 350 rear?
IMHO - that SL fighter is an absolute blast to ride. like freaking out of this world type of ride.
the ergos of the xx99 are already good for a sportbike, but a little more upright and easier control input? heck yeah! you wouldn't catch that bike with a regular SL in the twisties.
on the track (what it was originally designed for? well, yeah, fast sweepers and long straights, where wind protection is needed. but flicking it through esses or backing it into a 90 degree turn? i bet it's easier on the fighter...