I've had the six-wheeled Gators; and with the differentials unlocked, they don't turn too bad in soft stuff.
I used one for working out off the main road where I didn't want to get my truck all scratched up, they have a purpose. I also used it to move firewood around the yard, and for that they are very useful...no trailer to back up. One thing I found out was that when they are empty, they are actually pretty easy to get stuck...the one I had I used like a golf cart, just hauled me and some minor gear to/from the job site; it did not take much to get them hung when they are empty.
The main issue I had with the TH6x4 was the lack of ground speed...good for working in the yard, it sucked if you had to run any distance. And the TH6x4 (the newer/newest they last made) was a 17HP Kawasaki, it was alright on power. I wouldn't run much more than a mile or so with one, or you would be spending most of the time driving and less sawing.
As for hauling, just the simple fact you have the four tires on the rear will make them better for hauling in soft stuff...those rear tires are deceiving on the newer ones, they are extremely wide and have a squarish shoulder (read: wide footprint). The only time this doesn't work for your advantage is if the ground is uneven...going over a ditch for example. The rear not having any suspension doesn't allow the tires to float...but at the same time, it makes the unit more stable.
I definitely wouldn't pass on one if the price was right!