Pundy,
I am pleased with how they fly (amazed, actually) together. Mine is a 1975 182P so it had the Cessna 'cuff', but HUGE difference with BOTH. (The Sportsman's website shows the profiles of various cuffs for comparison.)
I do NOT see any loss at cruise. (A test pilot might be able to find some?)
I also wanted the increase in glide ratio that is claimed. I haven't played much with that, but I have to slow down well below normal Cessna patern speed to decend-It wants to fly.
So far significant drawbacks are $$ and width. If I had known I was going to do this I would have built a 45' door. That is water under the bridge. I painted a line on the apron and take great care putting it away. And it was yesterday's $$......

lc