Re: Why only one thermostat?
I agree, even in our 1 bed flat, having a single thermostat is really suboptimal. It heats the living room quite effectively, but leaves the bedroom freezing (the bedroom is north facing, the living room south facing). We can balance the radiators to some degree, but this just has the effect of making it slower to warm the living room - which isn't great either.
We have very unpredictable schedules, so the nest is useful, but we'd certainly investigate individual thermostats for each room/radiator in the future. This seems a lot more logical.