I had a Sundowner and really liked how it sat. The looks were not great for my Street Glide. Unfortunately, the seat pan cracked in less than two years so it had to be replaced.
I've currently got a Mustang solo which doesn't have enough back support unless I use a backrest. It's also proven to be uncomfortable on long rides unless I use an additional pad. Needless to say, the Mustang has been a disappointment.
I'm now considering going back to a Sundowner, or maybe consider a hammock seat. I tried one at a recent show, and it seemed like it was fairly comfortable.