I'm giving it five stars because it's by far the best tuner I've ever owned. Using the MANdolin sweetened tuning, all my mandolins sound wonderful. Using the EQU setting, it confirmed the tuning accuracy of the frets all the way up the fingerboard.

However, even though it's a great tuner, it has issues. In no particular order:
1. It's difficult to know when it's turned on/off. It really needs some unambiguous way of showing if it's on or off. (see also point 4)
2. Sometimes it's too sensitive. Trying to tune in a busy and noisy open mic venue, the tuner had difficulty latching on to the note. I've also noticed that if I put the tuner on a table, the display occasionally springs into life. I conclude that the piezo pickup is sometimes too sensitive. When clipped on to an instrument or on a flat surface, it can detect external noise and mistake it for a signal. Some way of reducing the sensitivity and/or rejecting random noise would be a huge help.
3. A device of such complexity and power really deserves far better than a flimsy two page instruction sheet. For instance, I only discovered the existence of Peterson Connect when I registered here to write a review. There is no mention of it on the instructions.
4. Another user's review mentions a "hidden" auto shut off feature. What is the point of a feature that no-one can find?