Roadie Tuner is another good product for guitarists, especially for beginners. You can connect it to your smartphone. Good idea for today’s population. Awesome for your friend. When I started playing, I had a pitch fork or pitch pipe. You had to use your ears. By using by ears to recognize these 4ths, it helped me in other musical applications as well. Of course I have since taken advantage of technology for efficiency and accuracy. An automatic guitar tuner is cool because it make tunings quickly.
A phone is required. The phone app is actually what processes the incoming audio signal to see if it is in tune or not. The winder is simply a small motor that is controlled via a bluetooth interface. It uses the phones microphone to tune acoustics and you have to use an adapter to tune an electric guitar.