As promised I took some images of the smaller or lighter Swiss army salt and pepper backpack from 1963 made by A. Mosimann. As you can see it lacks the stronger and reinforced carrying system and the closing flap with the leather buckles. This makes it about 2 kg lighter and a lot slimmer when not filled. The materials have the same strength and the reinforcements of the stitches are pretty much the same. Absolute superb craftsmanship I have to say, not one single weakness I could find on the construction of the backpack. All buckles or leather parts have got reinforcements on the other side of the canvas. The canvas itself is very strong but does not tend to break. I guess if you treat it with some wax it will be waterproof like a barbour jacket.
Speaking of the comfort I have to admit the bigger and heavier rucksack feels a bit more comfortable esp. when you plan to carry a lot of weight. But at the same also quite heavy and bulky even when empty. The closing method of the lighter one is quite strange at the beginning but quick to access and if you fold it it should be keep most rain away. So I would say a quite clever design. So if you need a stylish vintage backpack with rugged leather I would say there is no better one on this planet for around 30 Euro / 40 USD. Grab one as long as they are available.
For an earlier review of the bigger and heavier backpack have a look here: