This is a great size to have in my bag when I'm just going out for an hour or so; I always like to have water on me so I'm not tempted to buy it. Because of the size / shape I find it a lot easier to have in my bag than my traditional water bottle. It's still ridiculously expensive for what it is, but I decided to splash out as a treat and am happy with it (though would be too embarrassed to tell anyone how much it cost!).
Great stuff. Works well with all my notebooks and things. Small enough and shaped perfectly to not cause my bag to feel too bloated. Having it at work helps cut down on cups and I only have to worry about me using it!