You probably know the action in the Galapagos dive sites is usually deeper than 60 feet / 18 meters. As a rebreather diver you should know that below this depth an off-board bailout cylinder is required by almost every existing training agency.
As you might know, we tend to have strong currents here and a sling cylinder often increases drag. This makes maneuvering the already heavier and bulkier rig (in comparison to a single back mounted cylinder) significantly more challenging underwater.
Picture this: As current tries to rip the loop out of your mouth you experience the barnacles you hold to remain in place start breaking. With one hand holding your expensive camera, you only have another one to prevent your loop from exiting your mouth (and therefore inevitably flooding the unit) and to crawl forward to a place where you can hide from it.
The availability of bailout gas is a critical factor in such a situation; your bailout plan should not only include making it to the surface slow enough not to compromise your safety and therefore the overall trip, but also heavy breathing during that ascent. A minimum of 40cft / 5.7 liters of gas are required for a diver with an average SAC to perform such task.
In Galapagos Rebreathers we have 40 cft / 5.7 liter cylinders with DIN / YOKE convertible valves available for rent. This size of cylinder minimizes the drag when appropriately side-mounted on your rig. If renting a bailout cylinder is too expensive for you, maybe you should reconsider diving on a rebreather. Or you can use a standard 80 cft / 12 liter cylinder readily available from your dive operator. In any case, whatever you do please have off-board bailout gas available with you in every dive.