I have tried out a Bob Marshall (a friend let me borrow it) and to me it feels like riding bareback. You are a little more secure because the saddle has more grip than a slick, bareback horse, but the feel (to me) is the same. You can feel every muscle in the horse's back. If they tighten their back muscles, you can feel it. Every step, you are in tune with it.
I personally would worry about slippage because I have had bad luck with flex-trees and bareback pads with stirrups, so I am leery of anything that isn't solid feeling on the horse. But this particular horse was cinched so tight that I don't think it could have turned if it wanted to!
My assessment is that it is good for someone who enjoys the feeling of riding bareback. It was definitely comfortable. But I don't know the long term effect on the horse or anything like that.