Colo, the premium might look ok for medical. But what coverage does that give the fourth chid? Not the same as the other three is it? Is it enough? When the eldest becomes too old for medical cover, and you have only three in the scheme, the fourth child is still considered as an extra, for the extra cost and lesser coverage.
When you, your wife and three eldest kids get ALTs, you will be forking out for a firm ticket for child number four. Hope your not needing to travel too far. They aint cheap. When the fourth child becomes too old for ELTs (24) or ALTs (19) as appropriate, the fourth child will then become eligible for tickets.
Good luck with schools, but the other ones aren't that much cheaper.
Think long hard and be honest with the decision making on this. Once the skill test is complete, you have 5yrs to do or a bond to repay.
Good luck,
the don