Yeah, they are very dangerous. When I was up in school, we actually used climbing gaffs to climb power poles. Theres not much there, and if you dont get the right angles, you slip out and slide down. I always climbed without a belt, but I would recomend one. And in the bark, they are very dangerous. Make sure you practice and dont get to high when doing it. Rotate around the tree getting different angles and positions. If you have any questions, pm me. I am more than happy to help you out..
Ryan