I'm not sold on the diaper setups yet. Tried them years ago, just didn't work very well for me.
I can't find anything that is ultra lightweight. Depends on where I'm going as to what I'm going to carry. I have a LW wide climber that I have modified a bit, has a mesh seat and weighs somewhere around 11#, then have a lightweight safety belt that's 18-20 ounces. I don't use the climber much, generally a stick or two in the right tree with a few branches and I can get where I need to be with a light lock-on. Just depends on what kind of area you are going to.
I'm not aware of any lightweight climbers that you can face the tree with, if you are wanting to face a tree I would look at the diapers with sticks or a set of lightweight climbing spikes.