I flew into Quito en route to the Galapagos a few years ago and almost panicked about not being able to breathe. Mate does work! These days I fly often from sea-level San Francisco to visit my daughter in Montana. She greets me with a can of Oxygen, Nifty instant-air now widely available over the counter. I think I'll never go to high altitudes without it -- but probably you can't take it on airplanes . . .