The High Efficiency warp drive is an old idea in Ane memory. However it has not been implemented due to the necessity of a living brain behind the control system. This was done one, to them. They didn't like it.
The unrelated matter of RI development brought the idea of the HE drive back into the realm of the possible. Here was a sentient mind that had not just the processing power, it wasn't a hideous crime to ask them to take control of a warp core.
The advantage of the HE system is that it sips at antimatter. An HE system can get three to five times the range and power for the same fuel as the usual Starfleet core. The nanosecond control and fine tuning required make the drive the highly tuned sports cars of the warp core world. Starfleet wants trucks, rugged dependable and near unbreakable.
First generation drives were single core designs. These cores could get three times the fuel savings as a standard core. They introduced the warp control fin on the accompanying nacelles. They were installed on the Emerald class, The Euphrates class and the Unity class ships.
The Second generation uses a different nacelle geometry. They increased fuel savings to 3,5 times and used the first dual core system. This system increased the power available to the ship in emergency situations, abet at the loss of any fuel saving with both cores pounding away.
The third generation HE systems got five times the usual fuel efficiency when used in cruise mode.
Third generation nacelles with the dual control fins were also oriented so that the fins faced directly away from each other. This increased the speed and accuracy that they could manipulate the shape of the warp field.
High Efficiency was not left behind with the DiSodium breakthrough. the cores have to be locked behind sound and light shields, and the nacelles are slightly different, but the entire horned fleet has been converted.