I have that coop and like it very much. If my birds were confined for any amount of time, it's only good for a couple, but they free range and a bunch have decided, against my suggestions, to all sleep in it. I have no idea how they can be comfortable, but they are.
I would strongly suggest the following:
Add some coonproof/predator proof latches to the doors.
Waterproof it with some paint on or spray on stuff
Put it where the wind cannot pick it up.
I don't think it's nearly as awful to buy one of these as people make it out to be. I have built several coops, and I bought one of these. This one has held up just as well, if not better, than the coops we built and it cost way, way less.
The size is definitely an issue. You cannot let chicken math happen if you have this as your sole coop.