I have had one for years. You cannot backpack with them at full load for too long because they are not TRUE backpacks. They will hurt your back after a while as they put too much pressure on the shoulders (they do not have a frame). Plus, the zippers are difficult to use comfortably. Finally, the material will start to rip apart if you often use a full load when you go hiking.
Why I have one? Fits the overhead compartment of most airplanes.