Interim report after 2 nights sleeping on the thing.
it takes a lot of effort to blow it up, but the Downmat was also a pain, like giving CPR!
Lying on it, it feels very stable and supportive. It's warm to the touch, though probably not as warm as the Downmat.
It feels quite fragile, only time will tell.
I've had 2 good nights sleep on it. I'm sufficiently impressed to consider selling the standard one I bought and taking the hit to buy the Large model, I don't need the extra length, but another 10cm width would be less like sleeping on a plank.