The only problem I've found with my Torges type tree seat is that you have to be careful what type of tree you use it on. Slick trunked trees-maple, beech, holly, etc.-don't work well. I have to wrap the rope around the tree once to keep the rope from sliding down the tree when I sit on it. The other thing, be sure you have enough rope. A 12" tree has a 3' circumference, a 24" tree is over 6' around. I have about 10' of rope on my version.
These type seats don't harm trees. Many public lands and some leased ground stipulate that screw-in steps, nails, spikes, etc. aren't allowed-nothing that damages the tree.