I agree with this. In any race long enough to need to carry water I think the modern rucksack is a better option (Salomon 12 and 5 set being the ones I like) . The only very slight downsides I can think of are : potentially a very small restriction in breathing (probably no real effect though). slightly heavier / more material to soak water and sweat into. More skin covered making it a bit hotter in very hot weather. Although the Salomons are designed to be worn directly on skin ( hence the skin set thing) if needed.