I have to agree. They do look good, and more comfortable than sitting on the ground. And it looks like they are relatively easy to attach to a tree. But the price is more than what the average 'stump sitter' would be willing to pay.
I have a seat that I have had for years that has a belt that goes around the tree, then a 'camming action' when you flip the seat down to make it solid. And has 3 different seat positions to accomodate the angle of the tree. I haven't seen these around in quite a while and perhaps they quit making them. who knows?