Most rebreathers fall under the CCR category which in its self can be split further into two sub categories – Mechanical Closed Circuit Rebreathers (MCCR) or Electronic Closed Circuit Rebreathers (ECCR). The reason for these two sub-categories is mainly due to the fact that some people do not trust their life to a unit controlled by an electrical technology well underwater, others like me “trust the technology” and use an ECCR.

MCCR’s uses a mechanical valve of some type to feed a set controlled amount of O2 into the unit, such units as the KISS and the rEvo use this method. The ECCR has a solenoid that controls the exact amount of O2 required to maintain a preselected amount of O2 in the unit, such units as the Inspiration and the Optima use this method. The objective is to match the amount of O2 being supplied to roughly the amount the diver will or metabolise during a dive and both methods roughly attempt to do this.

The newer models of CCR units now come with a built in dive computer that will dynamical sample the O2 in the breathing loop of the unit and adjust the decompression obligation of the dive to reflect this amount, giving what is basically the optimum Nitrox mix for the entire dive.
CCR units are quiet and give the diver an unprecedented look at the wild life, no bubbles to scare them away, they also offer a much longer bottom time and a shorter decompression time for the dive. The units do though require advance training in their use and require a higher level of basic maintenance to be carried out. They also are more expensive to buy than OC gear and do have a higher cost per dive due to the consumables like CO2 sorbent and O2 sensor cells.

Given all the above I am still firmly of the view that a walk on the dark side will convert you to this new technology fully and unless you wish to spoil your OC diving for ever you should be avoid the temptation at all cost, once you cross the line there is no return.