Cylinder/system duration chart here:
1/ Mountain High oxygen system endurance chart
The MH pulse system is easy to use and economical on O2 quantity. I use one when making my annual gliding safari to South Africa, where operating heights are 10-18,000 ft and typical flight time 6 hours; not needing to refill the system daily avoids hassle (= delay on getting to the bar to rehydrate) although there is on-site refill there.