I have three original Duluth Packs, one #4 and two #3. They're great. Everything about them is well-made and heavy duty. I expect these packs will still be going strong twenty years from now. The only drawback is they're not waterproof. On the other hand it's a lot easier to carry a load in them than in my waterproof Seal Bags. Among other things the Duluth Packs have tump lines which certainly make packing easier.
These packs have been around since roughly when Christ was a kid and I fully expect they will be here for the next hundred years as well.