I do tree work all the time and i see no use for one of those things. I can trim faster with a sharp razor pole saw and not be anywhere as tired. I used one my friend has a stihl, didn't like it. Can't make a proper cut at the right angle with them half the time anyway.
Yardmonkey check out the forum on the International Society of Arboriculture , they have a tree climbers forum, pain in the butt to get on though. If you look through the other chapters websites some of them have forums too. One called the Knot hole discussion board ,pretty good, A recreational climbers forum also is treeclimbing.com.