The fuel flow has nothing to do with fuel savings, the reduced fuel load is the only thing enforcing a efficiency strategy. Strange how no-one complains when WEC has fuel tank cuts and enforcement of efficiency. It being an endurance series does not invalidate the point...
The fuel flow meter's sole purpose is to restrict engine output powers and boost pressures. According to Niki Lauda, the unrestricted Mercedes engine could easily surpass the 1200hp marker. Red Bull are making such a fuss about the faulty flow meter because it reduces the engine power if readings are off, and FIA want to ensure nobody gains extra power to fuel flow.
What I found a very interesting graphic where the "used fuel %" they showed in the race. You could see that DR's Red Bull was on the top of the standings there both times it was shown, Vettel being second, and the Mercs the most efficient. I'll have to check if these stats can be viewed anytime during the race, makes the race more interesting knowing this stuff.