This post, and many many many like it are why I firmly believe the medical bottles are the way to go. They cost much less to purchase, much less to fill, medical O2 is available almost everywhere (Medical suppliers, gas suppliers, Dive Shops), You can buy an adapter to fill from an aviation source (Aviation people will fill a medical bottle, but medical people will not fill an aviation bottle), they can be trans-filled if that is your cup of tea.