I believe you would want the harness for safety's sake.
With this design you're somewhat protected by an exo-skeletal frame where you could possibly load a hundred pounds or more on top with no added weight on your shoulders. I could imagine an Infantry unit using these to travel 50-100 miles in a day with full packs and still arrive reasonably fresh and able to fight. I could see commuters using these to negotiate tight European or Asian streets with their typical outsized loads weaving between gridlocked cars.
The quick-release harness would be a must, though.