The Britannia model is a solid model with a removable rear canvas, built for gaming. I finished mine in OD and painted the canvas in some horrible green that suggests that I might have been drinking my paint water at the time.
The Academy model is a finely detailed plastic model kit with quite a number of finely detailed fiddly pieces. It builds up into a fine looking model, though may be a bit too delicate to handle for some gamers. It comes with a canvas top for the cab (which I did not use), but does not come with the canvas for the cargo bed.
The Academy kit is a little longer than the Britannia model and the wheels look noticeably larger, but either is obviously recognizable as an M35. Here are the pics:
The Britannia model is to the left in the photos above, the Academy model to the right.
The Academy model is at the top in the photo above.
The Britannia model on the right with canvas cover on the cargo bed.
The academy kit comes with benches for the cargo bed, but I did not assemble them. They are very fiddly by gamer standards. I also left the rear view mirrors off and removed the exhaust stacks from the right front fender during painting, as these parts had no hope of surviving my handling on the table top.