Electric trikes can be a great way to get some exercise. It's comparable to riding a bike in that it primarily works your legs. The more weight you add on the rear of your adult tricycle with the basket, the more difficult it will be to move, resulting in a better workout.
However, some people may find the allure of an electric motor to be too strong to get a good workout. So, rather than giving up and using the motor, you'll need a lot of determination to operate your legs.