I have seen huge trees pulled with a Farmi winch. The only problem I saw was that the winch would pull the tractor if the tree was to heavy.
Like any tool, it only makes sense if you use it enough to justify the cost. I maintain 25 acres in VT and there is aways another tree to salvage. Most of these I can reach with my tractor and a chain. Occasionally I need to call a friend with a winch to pull a log out of a hole or swamp. If you cut trees for a living I would buy the winch. Otherwise, find someone who has one and pay him a few bucks when you can't get close enough to do it yourself.