I suspect that they have bought themselves a bit of a pig in a poke, as we say here. It will be recalled that BA deactivated the overwing exits, which means that the maximum number of passengers that can be carried is significantly less than those on 'whole' aircraft.
This means that the cost per seat being quoted by them is likely to be a fair bit more than that of competing aircraft - especially ones like Corsair's B747-300 which apparently has an eye-popping (and DVT inducing) 580 seats!