You have to keep the data in that class for a certain period of time. That's the drawback. You can access the data at that price as long as you keep it there for a long time.

So I suspect this is not a fully cold storage. That's why they can retrieve the data faster. Seems more like an economics hack (Longer commitment to keep the data, allows them to buy and operate the storage hardware/software at a cost that can be amortized against those commitments)