I bought this because I have a 3rd cage under the downtube and the water bottles that you carry there can be pretty disgusting, and I thought I might be able to streamline by emergency supplies. But really this is not any more useable than the disgusting water bottles.
This is not very tall-for reference about half the size of a Camelback Big Chill, but it is slightly bigger in circumference. So 1)you can't fit a lot in it, and 2)it is hardalmost impossible to get out of a water bottle cage because it fits so tight. I can't believe anyone could fit a larger tube in here and have an easy time getting it out if they needed it.
For me, this is perfect. I am usually ridding 65 miles or less, using one large water bottle. I leave early and will wear a light jacket when cool in the morning (summer or spring) and stash it in the storage container when it warms up. Also, an energy will also fit with a light jacket or vest, leaving more room in my jersey pockets. Works great with my bottle cage, it is held snug so it does no bounce out. Maybe the typebrand of cage makes the difference, works perfect with mine.