This is a great value bag, it seemed to be fully waterproof and could get a lot into this. Its 35 litres when full, you can get a lot more into this (as I did at the start of the trip with food) the only problem is that you can only fold the opening once when overfull and so wouldn't be as waterproof. At 35 litres full the openening folds over 2-3 times giving a tight waterproof closure.
I took this on a plane and there was no problem with the bag coming open in transit due to the 4 securing straps holding to together very tightly.
The only improvement would be for a large shoulder carry strap to be added as this bag is fine to carry by hand but if its full the carry straps are a little thin and soon dig into the shoulders if carried on the shoulder.
Great value bag, highly recommended.