its really marginal. Some say you use up to 15% less power, but real world testing on identical setups yields somewhere closer to 5% less power. In the end, after slight changes in pitch/cyclic you really won't have an identical setup anymore anyway, so i wouldn't really look at flybarless as a way to gain flight time per se, although you can get similar "pop" with a little less rotor speed gaining some efficiency. Mostly it yields a better performing heli that feels more "locked in" in all flight regimes.
In the end, the key to maximizing flight time is to get the headspeed the lowest you can while still performing the way you like. flybarless DOES help you here because with a traditional head, stability comes from higher headspeed and the gyroscopic forces on the flybar. with flybarless, with lower speed and thus lower average power draw, you can just increase the flybarless gyro gain to get the same stability. All said and done, you may be able to go to 1800 rpm and have the same pop and stability you used to have a 2000, but get better flight times.
kind of a long winded answer but its sort of a difficult question to answer with a yes/no.
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