Modified continuous-rotation servos are used extensively by roboticists due to their small form-factor, enclosed motor-gearbox, ease of mounting and high-availability. Some users keep the original drive electronics and the potentiometer feedback element but this approach allows for limited position control and velocity control / profiling. Others tend to remove them and use external control/drive boards and custom-made encoders. Ideally one would prefer to have the feedback element and the new drive electronics enclosed inside the servo.
