sanctum

[aknelsonone]

Regarding Sactum I have not seen it.
Speaking about the FFM (full face masks), there is only one or two models  really build for Rebreathers. One of them is the Draeger NovaR. The NovaR has some of the required features for RB Ron mentioned. The Draeger works with open circuit regulators well too.  I actually dive my Draeger FFM a lot very confi. in colder water.
The Buddy breathing is possible when everyone can keep cool. But hardly with a FFM it just takes too much time to clear a FFM.  This is one minor reason a lot of the modern RB mouth pieces are equipped with open circuit regulators. A stage with old fashion regulators is still the best back-up system when diving RB.

Andy