I've never used one and I have a boat to take me to where I generally hunt but I could still see use for one in certain situations to put me out into the middle of the weeds and shallow ponds in a couple of areas that are too mushy to walk in.
I think they could be a really great tool for a walk-in hunter.
I wouldn't mind having one for my arsenal. It's like hunting with a float tube, only it's solid and has a higher cargo capacity.