The £396 via the app will be the POUG fare for four people, £99 each. It is probably only available on the outbound.
My advice is that if you want lounge access and a nice experience on the flight that you take the POUG now on the outbound. That gets you the nice lounge at Gatwick, and the business class experience onboard. It's fun to do, at least once.
My experience is that when I get offered a one way POUG, almost always I get another offer via the app 48 hours or so before the return. So if you're hooked on business class and you don't mind a very poor Bordeaux lounge, you can decide then. Standard upgrades are usually very expensive (the "upgrade for money" option).
[posted simultaneously to Robespierre, same advice]