Back on topic though, the drawback to the system you specify means that you will have at least 3kg strapped to your bike (then add bits and pieces to hold the bladder, hose, etc) which will adversely affect the handling of your bike. The downside to my camelbak and my previous el cheapo version is that it makes me sweat profusely on my back. Despite the air flow channels that they design into the padding, I get hot and sweaty on my back. I regularly use my pack when walking into remote places at work, and I have to take a change of clothes in the car for when I finish as I'm soaked in sweat afterwards anywhere the bag is touching me on my back and under the straps. On the bike would be better and that of course would also depend on how hard you push things.