This isn't exactly a barberchair. When the back pops loose, that is a barberchair and kills many a person behind a tree. When the front pops loose too?, I don't think it has a name! If this is the one I think it is you can't tell from this close-up but he is on a ridge to make it difficult to move also. He was lucky, even though he appears skilled and experienced too. A few hours or more of funny video on youtube to laugh at trimmers and loggers when they get in trouble. Some very funny, some scary. Some guys learning about physics and gravity.
Buying and selling small pieces of land I have taken down 50-60 good sized trees although most fatalities are from trees under sixteen inches, always a thought! I had a lot 100X400 with neighbors on both sides and a bunch of gums that were 100-125' tall. Neighbor's homes on both sides, I had their undivided attention dropping those sixteen trees! I had a four or five ton John Deere at the time and we did the job admittedly with a few barber's chairs but I was aware of the risk which goes a long ways to nullify it.
My saw has a 32" bar but these days that is just so I don't have to bend over! I could take down a five foot tree pretty easily and have to clean up a stump bigger than that but I know my limitations are greater than the saw's. In the open I will drop a three foot or a bit bigger tree, close quarters, I call in the pro's!
Hu