I've used the Ortlieb backpack conversion gizmo on a couple of tours, I'm not that crazy about it. Ortlieb should stick to panniers, IMHO, and let someone else make backpacks. There are a lot of ultra light day packs on the market at varying price points that weigh within a few ounces of what the Ortlieb backpack harness ways, and are probably much more comfortable. Patagonia and REI offer them, and I'm sure there are others. I just got a Black diamond Shot daypack, it's worked well on a couple of rock climbs that I've taken it on, and I plan on taking it on my next cycle tour instead of the Ortlieb backpack harness.