The FPV is more useful on a HUD than on a PFD, but it is still useful. I don't know if I would feel that way, however, if I hadn't gotten used to it first by flying with a HUD as the primary instrument.
The absolutely best use for the FPV is in the case of unreliable airspeed. You can simply fly AOA using the FPV.
The FPV is where the aircraft is going, instantaneously. The perpendicular distance, in degrees, from where the aircraft is pointed, and the FPV, is you AOA.
Cruise is 2-3 degrees. Clean maneuvering or any maneuvering flap speed is around 7. I believe approach is flown at 4-5. Stall on a 737 is low teens, I can't remember the exact figure.