Helmet fire, out of interest do those crews relying on moving may displays carry a paper map (correctly amended) as a back-up?
We rely heavily on our CALF and CHAD system for keeping our maps as up to date as possible because we can fly unrecced routes (most night SAROPs) at 250' agl if the weather requires it and all obstacles above 250' should be marked on our maps with most below that height as well.
I don't know if the databases available for moving map displays match or exceed those criteria, especially for UK.
You are right, coming down from instruments to NVG at the bottom of approach is not a problem (as long as you are really visual) -I have, once, only seen the runway approach lights at night (and hence achieved the required visual references) at DH because I looked through the goggles - I didn't get properly visual with the lights for another 50' or so on the ILS but we had nowhere else to go and a very poorly person on board.
Good CRM is, as you highlight, essential to safe NVG ops - another advantage of having 2 pilots in poor weather is that one might have decent references even if the other doesn't so control can be handed over although this is only really relevant during very low level grovelling/hovertaxying.
Hum - I would love to be able to try a Garmin but you know how difficult it would be to get the IPT to agree to using it! However, all military SAR crews do have NVG and post 2012 (SARH) the civvy ones will as well.
The SAR Force started using NVG in the manner you describe with the crewman using hand held 'opera glasses' but it is f*ing scary flying mortal night techniques in the mountains when it is all black and trusting the Nav/winchop to talk you round the terrain!