As I recall, the sticker on it says that the max load is 70 pounds.
Balancing the load really isn't a factor. Unless you intentionally tried to load a lot of heavy stuff on one side, with nothing on the other side, you don't notice any difference in handling. I have never really paid any attention to balancing, and never had even a hint of problem with it.
The fact that it is a single-wheel design means that it tracks the bicycle - when you lean, it leans. If you can fit your bicycle with you riding it through a space, then the trailer is almost certainly going to fit through that space also. I looked at the "two wheels with axle" design, but this easily beats them for what we're discussing here. If you are looking for a baby carrier, then maybe the two wheel design makes sense. If you want load-carrying, rough terrain performance though, this is the design.
They aren't cheap, but I got mine as they were introducing a new model, so I got a good deal on it. You can also find them on eBay, but be careful - I watched some folks pay a higher price for a used trailer than I paid for mine new.
Confederate Colonel