Wife is reluctant to use "bottles".....first wife uses an electric wheelchair, and her mother used oxygen too "back in the day". The wife always got tangled in the canula back when she walked, and the wheelchair has a way of tangling up with cords, canulas, etc etc.
Also, when we were in college, there was an "interesting" problem with oxygen tanks (at least the ones that are 5 ft toll + or -). Someone knocked a tank over down at the university hospital. It lacked a protective cap, so the on/off valve broke off. The tank took off, went through the hospitals basement wall, and buried itself 12 feet underground!
Both those memories are just a little too vivid ;-)