Thank you, Rob, this almost works. I have tried all this and there are a few idiosyncrasies but the news is generally good.
It is only by using these systems aggressively in the real work environment that the practical problems come to light. When working alone at the computer the Intag system works brilliantly. It needs a silent uninterrupted work environment to maximise productivity. Then you receive a 'phone call and you need to discuss computer documents with the client. Now the Intags become a distraction and you need to get rid of them, but you have to put the client on mute while you restart your voice session to say hide intags.
Unfortunately, voice computing and client phone calls do not go well together.
The critical manual override, as you say, needs to be the hide Intag key.