I trail ride in a barrel saddle. I prefer the deeper, secure seat and being quite snug in my saddle (I have a 14" seat). My barn's trainer sat in mine and liked the "pocket" it puts your butt in. Unfortunately, mine's not super cushy, but I don't mind it and if I did, I could buy a pad for the seat.
I've not had any knee issues with it with my good knee. I messed up my right one in 2008 and hurts regardless of what saddle I ride in, but is fine as soon as I get off and walk around.