D'Addario nailed it with this product and is excellent in every point. I've tried Snark and the Uber Tuner, and prefer this a lot more. What I like:
Small - Turned out to be smaller than I thought based on the pictures, but this is not a bad thing. It means that that is super light, and out of the way.
Discrete - One main reason I like this tuner is it can hide behind the head stock and the audience only sees a tiny clip. Very discrete and professional looking. Other tuners look like a big potato chip bag clip hanging on your head stock
Stays on always - The ratchet mechanism works and stays on firmly. I have no fears that it will fall off. Because it is small, you can leave it on 24/7, even when you put the guitar down or put it back in the case. The tuner practically just becomes an integral part of the guitar. This is a HUGE advantage that you will begin to appreciate over other tuners once you use it. You never lose the tuner, it's always on when you need it, you don't have to waste time taking it off, finding it, putting it back on, etc. Because they are affordable, you can easily buy one for every guitar you have and leave it there.
Instant on/off and accessible power button - Press the button and it turns on very fast and its ready to pick up vibrations almost immediately so you're ready to go Press the button again and it turns off right away. The power button is also very accessible and easy to press since the tuner rests firmly against the head stock. Some tuners annoyingly make you hold the power button for a few seconds to turn it on or off
Screen is small but bright - I was afraid that the display would be too small, but it is plenty bright and can be easily read. It changes color depending how in tune you are
Accurate - The in tune indication has a very tight tolerance. It jumps around a bit because of this tight tolerance, but even if you are just around ball park, your guitar will still sound in tune. Other tuners I have found has too wide of a range for the "in tune" position. My ears are particularly sensitive to my guitar even when it is slightly off.
This product exceeded my expectations and I will no longer look anywhere else.