I’m a huge fan of these and have two of them in different sizes. They are basically slim rectangular prisms in shape and make for really efficient use of space in my bags. Super handy to carry a decent amount of water but not make my bags bulge. The A6 size fits perfectly in my Side Kick and the Slim fits perfectly in my Synapse 19/25 water bottle pocket.
Agree that they are a little expensive but since getting them I don’t use any other bottle, using cylindrical bottles now seems so inefficient packing wise!
In terms of being leak proof, they have not leaked on me once in the last year of regular use, however the design is a very simple lid screwing onto a groove. So you would need to make sure you have tightly screwed the lid on.
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