I have a Charm which carries 1.5 L. That means 1,5 kg if totally full.

I had bought it for running and tried it for the first time today. I'm bringing it back; I really dislike having the whole thing on my back. I'll get the waist-only model.

I could totally imagine it for mountain biking, though. But for the road, I much prefer bottles on the frame, because otherwise my back tends to get really wet.