I use one all the time in the winter for pine stand management. For pulp trees its great. For hardwood loads and logs on any terrain that is hilly, forget about it.
A great tool for the landowner harvesting firewood. But at the cost of the machine you could buy enough firewood for a friggin' lifetime.
I use a Kubota RTV for forestry work until the snow won't allow. Then the Iron Horse. Don't get me wrong. Its quite a rig. But it can also be quite a contraption, sometimes more of a hassle than its worth.
Be great for moose and caribou outfitters in the north. Handles wet, boggy, terrain well, and with the log bunk trailer it will hold quite a load of hind quarters. It will go anywhere you can walk basically. Can winch it up and down hills. And pull trees (pine mostly) down to the ground with it when they hang up.
Pretty simple design, but needs some refined engineering in my opinion.