I have one. It might someday be handy with my recently acquired mountain bike. As I understand it... those bottles can easily bounce out of the cages during aggressive mountain biking. I am really a road bike kind of guy. But trying to expand my season a little bit with the mountain bike.
When riding my road bike I know I am never more than a handful of minutes from a pop machine (they also sell water now), or a park with a water fountain, or a gas station (they too sell water), or neighborhood or grocery store, or coffee shop, or fast food place.......