Darrel,
Yeah, it's a nice thing to have but not essential to the pilot's
health or safety except the extreme cases. Not sure how expensive is
an oxygen system integrated with an oximeter (on-demand system) but
unless one is concerned about running out of oxygen, there is no point
of messing around manually with the regulator while flying. I'd be
curious to see how many pilots use the oximeter while using oxygen.

Hai Longworth