aparently his expert status is in mechanical systems but he has been felling trees for firewood for 30 years... wrongly it would seem
one of the main things i noticed on this video which may or may not be contraversial is his take two steps back. IMO it should be two back and at least one or two to the side. behind a cut tree is a danger zone, as is in front of it, and you should avoid where possible, being in either of those areas while it goes down.
a friend of my felling instructor sadly passed away when he put his felling cut in a tree, retired some 30 feet behind the tree but couldnt pull his saw out so left it in the cut rather than stand there fighting with it as the tree went over. the tree spat the saw and it flew the 30 some feet and smashed the fellow in the face.
when we did our assessment, if you got in those dangerzones, if you swapped sides of the tree to put in your back cut without leaving a suitable perimeter, you were toast, failed. It's kept me safe thus far
jim