Martin Hellman wrote:

Just so I'm not accused of being a MH schill, I agree with the two
downsides that have been mentioned: higher initial cost and only legal
to 18k.

I'm repeating myself, but: Believe it or not, there's actually life
outside the USA! The original poster posted with an *.ch address. If
he's really living in Switzerland, as this address implies, then there's
absolutely no legal concern. There are *no* regulations for oxygen use
by private pilots here.

Stefan