Been looking back and forth for a while, from what I've read:
-Changes driving dynamics for the better, boost always on instantly. People seem to love them now.
-Much smoother, no jerky clutch engagement
-Cheaper as it's much simpler, no need to worry about clutches and bearings etc.
-Baseline IATs run about 10-12°F higher at best. Really need max cooling already sorted if you want this to work.
-MPG goes down a couple of points
-Supercharger theoretically will wear out faster
-No actual power or performance benefit
I think there used to be a tuning hiccup issue when these first came out, but nowadays I'm fairly sure it's sorted. Everyone that has them seem to use RaceIQ, they come highly recommended and the hiccup seems to be gone.