hi andi,
we had one diver here some weeks ago diving with a fullface masc and a fx1 bluefin housing ... but he had a monitor on the back of the housing, so i don’t know how it would be with the viewfinder ... but he said it workes “allright” ... still he was using the monitor.
just by looking i was not convinced of the concept ... if water is freezing ok. but otherwise ... somehow just in the way. after some up and down current he struggled shooting and equalizing at the same time and gave up and took a normal mask and his octopus ...