2 Things
1. Since its computer controlled, the generator can vary the speed of the engine based on the applied load. This has a huge impact on fuel economy. It is common to get 12 - 15 hours of run time on 4L of gas.
2. Efficiency of the inverter. No other generator matches the WATT/Weight ratio of the Boliy. This is due to the inverter using the engines power more efficiently.