My normal platform is ameristeps on an over center buckle strap. On the wrong tree, they can slip. I like having the stirrups with me either way. A couple of screw steps or tree bolts are another extremely portable option.
Stirrup comfort depends upon padding and the firmness of your boots. When I have used them with a saddle and needed to stretch, I might hook up my linesman's belt and stand up all the way. They are definitely better for sitting than standing. When you lean or stand, your feet are braced against the tree.
The knot I tied in the middle actually holds you off of the tree.
Add some kneepads or you can relax by just hanging and straddle the tree.
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