@wetb4igetinthewater metal on metal doesn't mean a bolt snap to a d-ring. Metal on metal means you have a soft connection between the bolt snap and whatever it's tied to. Don't thread your SPG hose through a bolt snap. Don't screw clamp a carabiner to your tank for a lower sidemount attachment. Metal to metal is fine as long as you can saw through whatever is holding the other side. Otherwise we'd never be able to clip anything off to anything else.
In zero viz all of your communication is through touch contact. Go, stop, switch sides, entangled, give me gas. You either know where your second stages are, or you don't. And you can't see. And your buddy is telling you he needs gas. (Which btw I have yet to actually experience in a cave outside of training, you REALLY have to screw up for that to by the case)
One method guarantees you know exactly where your second stage is, and worst case, with a stuck bolt snap, you can still pull your short hose out of the bungee to donate and deal with your stuck long hose. Cut it free, even if you have to breathe with your head a little wonky for a minute. It's awkward as hell, but you're both breathing, and you have time to sort out your issues.
The other puts your long hose potentially 7 feet behind you, so now you've gotta grab your hose and pull it forward, inserting 7 feet of hose directly into the middle of an already precarious situation. And you're hoping that the same stuff that has destroyed the visibility, hasn't also packed your second stage with so much clay, sand, and mung that it ceases to work. Or you hope that it hasn't decided to act as an anchor in between a couple rocks preventing you from even getting to it. Or you hope that you haven't smashed it in the cave so much that it's blown all of your gas. Only you can't be sure of any of that because it's been trailing 7 feet behind you since your last gas switch.
At worst, the first method is just a little awkward for the brief period of time it would take to cut off the cave line with your buddy at the rather intimate distance of roughly two feet away. At worst, the second method ends up with your buddy being unable to breathe because the gas source you intended to donate is nonfunctional. All because a component that, by its very nature, is designed to fail, failed as designed.
I know people advocate for breakaways. I know some pretty well known people advocate for breakaways. I don't. And the one reason they can give is outweighed by a boatload of others. I sure as hell won't dive with those people in a true sidemount dive. They can go solo. I can go solo. But I sure as hell won't rely on them for gas. It's a liability. It's like people who rally against CCR's. You introduce 3 potential issues but you solve 20. "OH BUT YOU'RE GONNA DIE ON ONE OF THEM DEATH BOXES!"
The fact that this even comes up is because somewhere along the line sidemount became this bandwagon that everyone who wanted to be cool decided that they had to use, regardless of whether they had the need, capability, or cerebral aptitude to use it correctly. Agencies decided that it was a great way to make money so any OWSI could self certify as a sidemount instructor and post fancy Jesus pictures to instagram. Of course none of those people see anything wrong with their students trailing their octos behind them in the breeze, so why should it bother them if that hose happens to be 7 foot long?
Breakaways are stupid. If anyone can post an irrefutable reason other than "OW SM divers suck and can't be expected to adequately perform basic skills" I'll eat my hat. /rant over