That “one in none, two is one” only applies to things you’ll die without. Air supply qualifies, compy does not. If my computer fails underwater I’ll make my way to the surface, hang out a while at about 10’, and I’ll have the rest of the day to get a replacement for tomorrow’s diving. Don’t need instrumentation for that!Whilst I understand your context, dives change and become a different context
So then the biggest bottle thats comfy would be good in case you choose to go deeper
without having to surface first, and grab a bigger pony, also the second computer helps
as if your primary computer, fails, you then have until your secondary computer, fails, to
continue your dive although I can not imagine a valid reason for a direct no-stop ascent
and it is not in my vocabulary, I had to copy and paste, from your post, unless I suppose
you've lost track of time and don't have a pee valve and or done an uncontrolled ascent
squirt extra oxygen in your auxilliary bottle that's where you become autonomously solo
Missing part of the days diving would make me sad but it’s not worth lugging an extra piece of kit everywhere forever to prevent it.