All Nouveau Contour devices (unless it’s a wireless device) consist of a power unit, a handpiece, foot pedal and power connector. Your handpiece, foot pedal and power connector plug into the power unit. The power unit determines the speed of your needle.
In a work setting, some machines are more portable than others. If you are traveling a lot, you may consider that when choosing a device. Are you a beginner or more advanced PMU artist? Consider a device that comes with more presets, or a device that has more needle configurations if you’re more advanced.