Well I opted for the Camelbak Hydrobak, mainly beacuse after looking around all the possible retailers in Nottingham (running shops, cylcing shops and outdoor shops) I could not find the Flashflo. I was suporsed that the running shop didn't stock it, only the Catalyst, especially since it seems to be so popular. So I thought i'd try the backpack design. I went running yesterday and did 19km with the backpack and it felt fine, no significant chaffing so happy so far.