<<I must miss something here. The quick donning masks you can find on a 737 or A320 are "demand" but can be regulated to Normal, 100% or Emergency (emergency being positive pressure regardless of demand).
What's the difference with the Concorde apparatus>>
Presume like the things RAF guys tried at N Luffenham in Aircraft that went 45'K+. It is nothing like the A320 "positive pressure" that blows a little 02 at you... These things positively "inflate" you at the pressure required to absorb the O2, and it takes all your concentration (and effort) to "blow out", ready for it to make your next breath.
And not really worth trying to "talk" in this process - get on with descending!
NoD