The hybrid option is definitely a good way to go, especially if you're willing to do the fiberglass work to save the labor. A lot of people do this to meet code while getting the benefit of the sealing characteristic of the foam. Even an inch of foam has vast benefits in air leakage prevention. I've even heard of people having closed-cell sprayed for the first inch and filling the rest with open-cell. The contractors don't especially like that because there is a changeover that needs to happen or they need to make two trips.

If you spray your roof directly with foam, it will prevent condensation problems on the underside. One thing I would be sure of is that they do it while it is relatively warm. Below 60 degrees substrate temperature, some foams start to lose their adhesive properties. Especially when it's metal because it acts like a heat sink. We have specially formulated foam for colder weather/substrates that looks bad when sprayed above 60.