Oops - forgot to mention that. The reason I've got tons of O2 cells lying about is cos if you're sensible you change them every twelve months. And get a spare to be on the safe side. So that's £200 down the swanny every year whatever you do.
However the more dives you do, the less skewed the cost equation is. Truth be told though, you've got to get shitloads of dives in to justify the financial argument - you buy a CCR because it makes sense to you, not cos the numbers add up.
AFAIK Helium makes no difference whatsoever to O2 cell life but they don't like CO2. My Dil tin always has a medium/strong Heliair mix in it for the simple reason... why not? Though I do miss being narked at 35-40.
