Why a Class A 're-breather' when CAP1034 clearly states that they add to the buoyancy of the wearer when you need it least - ie, inside the cabin/cockpit.
Now a Class A Compressed Air device would be solution - and does not require 'special' training as how deep do you think you are going to use it?
Personally, not considering the pax (in this respect) as they have been equipped with a far greater level of safety equipment than my industry has afforded me.................