Another consideration is the flight time of BA2 vs the alternatives. The A318 is slower than the widebody jets used to LGW and LHR. A quick check against FlightRadar24 suggests BA2 spends roughly 30 mins longer airborne. Deducting half an hour for both the ascent and descent suggests an extra 10% sleep opportunity on BA2 than the alternatives. This benefit may be offset by the earlier departure time.