I dive the Neptune Space G Divers & carry an independent gas supply, a Pony-13, Pony-19 or Pony-40. A brand new swivel connection blew the O-ring, during its first dive, during the predive, upon final connection, before water entry. It passed training, predive checks & disconnects but still blew. It came new, out of the package. I had to remove it, to start my dive. I don't recommend the swivel.
Diving a single tank, like an AL80, necklace your standard full length hose & OCTO. It can also be used for your buddy's OOA. Don't short hose it, it needs to be long enough to provide gas. You retain configuration this way.
Diving double tank, necklace it again, if back mounted or you can opt to long hose style your bottle/sidemount, in a carry configuration.
IGS/Carry/Bail/Stage/Sidemount configuration, whichever you wanna call it - leaving it stowed is last because you have to get to it. Longhose style, with standard hose length and necklace it. If no necklace, wrap it around the back of your neck & let it dangle in-front of you & dive.
I'm one "for" carrying a bail-out bottle, with an FFM. I necklace an OCTO & carry a pony.
MY SWIVEL BLEW TOO ON 1ST DIVE - Welcome to the club, throw it out