I bought this as a budget way to get both a hydration bladder and a new day sack. It certainly isn't big enough to be a true day sack, but then that isn't what it is sold as. It is however perfect for carrying items such as waterproofs and fleeces when out hiking, with of course 2 litres of water to keep you going.
The helmet stow compartment has enough space for a climbing harness & boots to go to the wall with, and the pockets at the front are ideal for both wallet and camera. The straps are comfortable and the ventilation back well designed.
Overall, it’s a perfect addition to a rucksack collection, fitting in where you need to carry a few items but just the bare essentials.