The chestmount CCR / twinset config, despite being super easy to add onto a OC twinset config, seems like merely a suboptimal convenience wrought onto existing OC methods.
It looks like a very natural and modular progression at first glance, mostly because CM units are marketed (correctly) in the US to the large cohort open circuit twinset tech divers. It's also very straightforward to build, fill, don, and dive a manifolded twinset (plus it looks like a cool jetpack.)
Twinset divers will also naturally feel like they can just ignore the CCR and revert to their OC training if there is a problem underwater, which also probably makes this config easier and faster to teach.
But was a open circuit twinset approach actually optimal for all of these divers in the first place?
This is debatable, though still default by tradition & agencies. It has merits, though in-water 3-valve twinset valve drills aren't actually that relevant, unless you're someone who regularly bashes into cave and wreck ceilings. Proper equipment maintenance schedules + adequate pre- and in-water checks of valves and regs is better approach to safety than assuming a manifold solves everything.
There are highly usable alternatives to relying strictly on manifolded twinsets for open circuit, including no manifold, 2+ cylinder sidemount, or even carrying an extra S80 stage or two with a "single backmount" config at a diving location that doesn't stock twinsets.
An added benefit of side-mounted or non-manifolded bailouts, for those properly trained, is that they don't necessarily all need to be the same gas. A twinset of the same gas is often excessive and/or not the ideal gas plan for CCR bailout, given the same total number of cylinders carried.
The experiment failed….I’ll only ever be putting either my JJ or a single on my back in future.
Same here. I definitely did not dabble into chestmount to "go heavy" either. There are already CCRs that are proven to do this better--JJ-CCR being in the top 5 for sure--more reliably, more safely, and more fault- & flood-tolerant than a chestmount / twinset config can.
People can and do go to 100 metres and beyond in CM/twinset configs, and can do so competently and safely given sufficient discipline/maintenance/training, but it is definitely not a 1:1 replacement nor necessarily an objectively better/safer/more optimal config for doing so.
But maybe chestmount + twinset config is just another stepping stone to a chestmount + a JJ/rEvo/Liberty/XCCR/Fathom etc dual config
...in which case the twinset still gets ditched
