This thing is so deceptively simple. Mine is a size small, I do not think I would appreciate the larger model, but who knows. Anyways, for longer routes (in-a-day Grade IV/V walls or free climbs, car-to-car epics where water is not an issue, etc) this device makes it trivial to carry sunscreen, half a liter of water, a headlamp, windshirt, and a snack (eg. clif bar or a packaged burrito) without cramming your pockets full of stuff. The pack itself has proven very durable for me, and the attachment mechanism is well engineered (velcro + fastex). I suspect there may be issues attaching it to some harnesses (Yates and modern Petzl designs come to mind) but if it fits your rig, I believe it represents a good value, and may force you to climb better by going lighter.