Which is NOT a feature of liquid-fuel rockets?

The option that is NOT a feature of liquid-fuel rockets is low cost. Liquid-fuel rockets are typically more complex and costly compared to other types of propulsion systems, such as solid-fuel rockets. This complexity arises from the need for tanks, pumps, and sophisticated engine designs to manage the storage and pumping of the liquid fuel and oxidizer, as well as to ensure the proper combustion process.

In addition to this, liquid-fuel rockets can exhibit potential instability during flight due to the nature of the fuel and how it is managed. The handling of the liquid, especially under varying gravitational conditions during ascent, can lead to issues if not precisely controlled. Therefore, the high cost of development and operation, along with the complexities and potential instability associated with liquid fuels, firmly situates low cost as an incorrect characterization of these rockets.