No need to let go of the steering wheel to get to the water bottle, unscrew the cap, have a drink, put the cap back on, put the bottle back at its place.
OK, OK, I believe everyone loves their tubes and bladders. I'm just kind of blown away that people on a forum who have discussions on how to amputate their own limbs in the wilderness, or how to start a fire by rubbing their fingernails together, or whatever, are saving themselves the exertion of unscrewing a bottlecap. ;-)
I'm sure it's probably one of those cool gadgets that I'll mock until I actually try one...
Dave