remember that the RB80 is a sCR, so basically a gas extender. Very different than a CCR where the gas that you have on your back is unlikely to be breathable for long, especially at depth.
also remember that with these agencies, it is all team diving where the team is theoretically diving nominally identical gear. I.e. if you have to start sharing air with someone, you have had at least 2 major failures that have rendered your gas inaccessible. Not that likely to happen, and beyond what you would normally plan for.
All of the backmount CCR cave divers that I know that aren't diving with the GUE style rigs *i.e. the "normal" rigs with either o2/dil on the back, or dual O2 on the back and dilout on the sides* have at least one tank with a long hose on it on the off chance that some poor bugger needs help that isn't part of their team, but also on the offchance that you have to or choose to dive in a mixed team. Doesn't really change that much of the gear configuration, for anyone. These guys will usually have sidemount bailout and in this case, instead of the long hose doing a modified hog loop like it would in OC sidemount, it comes straight up and clips to the right shoulder d-ring with the left hand/short hose bottle going up in the normal suicide strap routing. Short hose is still "my hose" and is on the left, consistent with OC sidemount diving. Long hose is still on the right, arguably where it should be with a "normal" regulator so the hose doesn't cross under the diver in an OOA event, and is clipped off for easy deployment if it comes to that. If they have stages, the stage goes out first with the reg going to the diver and then the whole bottle. If they need more, then the long hose is available.
some of the sidemount CCR guys that I know largely have the breather on the left, and the right bottle is the normal long hose tank from sidemount configuration. They keep it clipped to their right shoulder d-ring. Kind of a **** picture, but this is Edd Sorenson in the Sidewinder which basically acts as a bmCCR with sidemount dilout. You can see the left bottle regulators in the "normal" routing that comes up around his neck and is on the necklace, and the long hose comes up and is clipped to the right D-ring. Others dive it with the breather on the right and a dilout bottle on the left and run the long hose on the left and clipped off to the right d-ring. Not as easy to access if you have to donate as just having it clipped off, but easier than in backmount because the loop hoses are only on one side so you don't have to remove the loop from your mouth, just reach above the hoses.
Pros and cons, but some of it is CCR specific in terms of where you put which bottles. I.e. SCR like the RB80 or CCR modded like the GUE JJ with two big ass drive/bailout bottles on your back, bmCCR with dil/o2 on your back where you really aren't going to be able to share gas out of a 2l/3l bottle for very long, bmCCR with dual O2 on your back and dilout bottles, or smCCR with one dilout bottle.
Some of it is determined by whether or not you are diving in mixed teams, either planned, or unexpectedly and would have to share out of your big bottles or you are diving with bottles that are easily passed. I.e. in an area where you only have AL80's, I would just as soon plan to pass them around like stage bottles than try to deal with a long hose.
Some is personal preference and what you figure out works for you and your buddies. It's been a big point of discussion for my dive team on how we want to handle it and we still haven't settled on how we're going to do it, but we know we need one for the warm fuzzies that it brings and will figure out how to manage it eventually
