At high magnifications, the vibrations caused by even touching the focuser make the image un-viewable and the target rapidly moves out of the field of vision. Focusing is near impossible.
Motor focusers use a small stepper motor to control focus wheels. These, when activated, can turn the focus dial smoothly without causing any vibrations and allow for the target to remain in view. The also allow for very small adjustments to be made, which cannot be done with an unmodified focuser.
I have purchased and installed the SkyWatcher Auto focuser. Despite being called "Auto", this does not mean that it automatically focuses but instead is motorised. The package consists of the motor, control unit, brackets and screws. The installation was very easy, taking only 3 minutes and only requiring a screwdriver. The control box, although large, functions perfectly with two buttons for in and out focus and a variable speed control. Even at high magnification (100X) there is no visible vibration caused by focusing.