I have walked over a 100 km spread over four days with a backpack like that, and did that multiple times, for a survival kind of thing.
It's surprisingly comfortable, and the weight can be distributed quite well if you pack it well. Of course it's not close to a real backpack, and you shouldn't carry more than a few kilos with it, but in an emergency I can absolutely recommend this. Much better than a knapsack on a stick over a single shoulder.