Things to know about a motor when setting up a circuit?
You will probably not find enough information to do any kind of engineering analysis to select an electric bicycle conversion kit.

Strictly speaking efficiency for a vehicle is mechanical power output divided by electrical power input. Input power is equal to output power plus losses. Losses include electrical losses in the controller and motor and mechanical losses in the motor and drive components. Purchasing the most efficient battery, motor, controller and bicycle parts will mean less of the energy stored in the battery is lost and more is used to move the bicycle and rider.

The mechanical power is used to move the bicycle and rider. On a level surface, all of the power is used to overcome the rolling friction of the tires and the aerodynamic drag acting on the rider and bicycle. Aerodynamic drag power is approximately proportional to speed cubed. Higher speed means greatly increased drag and more energy used for a given distance. When climbing a hill, energy is used to raise the total mass to a higher elevation, but some of that energy can be later recovered by coasting down hill.