You do NOT swap primary sidemount tanks in the water. No one actually teaches that as a practical means of sharing air. Again, come and actually cave dive and try it, you share air on the long hose. One required, not two, no primary bottles move. Stages move, but that's it.
So, from the mouth some 50% of the time.
Yes, CCR adds complexity and I'd say tinkering with the gasshare protocol definitely qualifies for that category.
I'm not willing to carry over this one to O/C.
I know that you do not swap tanks in a gasshare, from one of our previous discussions. I'm saying that's one of the gasshare solutions I too am not attracted to, handing off tanks - so are two longhoses and inconsistent gasshare protocol in O/C.
As for static primary tanks: I do dive a rig where all bottom tanks and stages are identical and interchangeable. I see some benefits, but:
In terms of which tanks to choose on that rig, it's clear that there's a drawback in the lesser volume if choosing AL80s, as you say. I don't disagree with that.
I just find them easy to handle, which is something that I also care about because they're not static on my rig.
If you're keeping your primaries static, sure, why not go with the biggest you can find if you're not moving them anyway, the bouyancy works out and you're comfortable.
Fair enough. But mine aren't static is all.
If I
need different tanks for a specific dive in a specific place, I'd rent different tanks.
Like I said, if I find myself in Florida, rest assured I won't have checked 4 AL80s in my luggage
Conversely, you won't find any LP121s with a dive shop I've ever seen in the region I live in.
15L 232 bar steel, sure, but... nah.