When I was in high school, I played guitar roughly 10 hours a week. I took a class Monday - Friday, and I practice at home, at church, and sometimes during my lunch hour. In spite of all of this practice time, I never got a good handle on tuning by ear.
I wish I had something like this little tuner in high school. It clips directly on to the guitar, and you pluck a string. As long as you're somewhere within the correct key, you see the name of the key pop up ("E") and then you see if you are flat or sharp, and you tune accordingly. It's simple, it's intuitive, and I really wish I had this 15 years ago.
I like the easy to read colorful display, and I like that it can also tune a Ukulele, which I am hoping to learn how to play this winter. The only thing I would really love would be a small drawstring bag to store it in. All in all, a great deal on a simple gadget - I love smart, simple tech. This is a winner for sure.