As long as your in decent shape and have a little strength, climbing with the open shot is fine. You ab's will be sore from it though, it really works them. I actually have an older summit sit and climb, and for some reason I always use it as a hand climber too, I don't know why. I guess it feels more natural for me.

nodog, as far as the summit mat, are you sure that they stole that from you? I've heard of people using something similar for quite a while now. Maybe they did, I don't know.