Final update from me:
Spoke with AppleCare yesterday and explained the problem and steps taken so far (above). They confirmed I’d done everything they would suggest and were happy to talk about service options or returning under the 14-day remorse period.
We worked round the peraonalization issue/bug using the terminal steps here (https://support.apple.com/kb/HT211983), although predictably it didn’t fix the SMC error.
NB: The Tech also did seem surprised I’d gotten the personalization error given this should be fixed in 11.0.1 and asked if I was sure the unit came with 11.0.1 installed (which it did).
Most interestingly though was I heard from my other friend receiving a unit this week, and he too has the problem. This seems at odd with my other friend who says he can’t observe the problem in his unit received Wednesday.
As one last roll of the dice (and given the machine needed a full reinstall for my own setup anyway) I did a revive and restore from another machine using Configurator 2. This includes firmware too so should cover all bases. Alas the problem remains.
This probably exhausts my efforts now. It was interesting but now I just need to decide if to keep the machine. I likely will but I’d have preferred both my friends to have observed it, thus confirming it affects all units and is almost certainly a software issue.
Best wishes.