I got interested in them awhile ago, Didn't read the whole "article," so maybe this appeared in it somewhere:
(1) I understand you can refill them at dive (SCUBA) shops. Spare tanks advisable.
(2) Common lore is that air rifles were taken along on the famous Lewis and Clark expedition. (Manually pumped.)
I finally decided to just stick with my .177 Feinwerkbau air rifle, even though I did not have much practical use for the little projectile on the farm. However, a powerful quiet high-caliber air rifle might come into its own for certain situations if the trajectory is very well known and range estimation is flawless.
Cape Buffalo? You'd have to hit them in the eyeball or earhole. And so much for the sportsmanlike concept of a clean kill.
Terry, 230RN
REF (One of several):
https://en.wikipedia.org/wiki/Girardoni_air_rifle