My 60 lb lab carries two of these, one on each side of his pack when we hike. 0.6L x2 is plenty for most environments—just refill from your main pack if you run out. It keeps the overall system light while allowing him to carry his own gear. Not too big, barely takes any space in his pack so there is room for his med kit, food, a 15’ line, etc. The only observation (not really a complaint, just an observation) is that the threads are not standard (like a SmartWater bottle), so it won’t connect directly to water filters, if that’s important to you.