Some good responses. Grateful for the advice about coming to a stop - obvious really! I agree that, as you get used to the system, you can finesse your pressure on the brake pedal especially at roundabouts and, in time, get quite good at not triggering the idle stop in these situations.
As regards engine wear, I realise these systems are relatively new but is there any evidence of premature wear. The battery and the starter are uprated and not all the oil will have drained back down into the sump - there will still be a protective covering - it's not like starting from cold every time.
For me, the CO2 stuff is secondary (we need to reduce CO2 but these systems are not a game changer), the real impact is in emissions at pavement level so I think they have a role to play in improving air quality.