I use it since last week.

Features:
- True Bypass
- Power 9v + supply output to power other pedals 9v
- 3 tuning modes: tuning "all the strings together" automatically recognized when you play all the strings at once. We will enter the tuning of a single rope "when playing an open string at a time. There are two types of display are selected by a small "button" for this mode: The display classic type boss and a more accurate display type "circular" can be seen on the video demo QuickList (my preferred method!).
- There is a USB socket at the rear of the unit, which is intended for technical service if the device fails. (I think) I have not tried to connect to my PC!
Like:
- The look at the iPod it's very design
- The footswitch from the Boss TU-2
- It provides power to other pedals. I feed with two distortions, nickel it works, I have no breath.
- The accuracy of the display with tiny LEDs
- Different display modes. Give a string at a time or all at once. It allows to quickly see if a string of tune without having to play all the notes one by one.

I dislike:
- None yet. We'll see about reliability, which is the highlight of the Boss.

It's a great tuner, very fast (no waiting time), very accurate, looks nice, air-solid ...
I tried the TU-2 Boss from home. The display is less sharp / clear, because LEDs used his larger and have a space. I have also found less reactive.
I have not tried the TU-3.
I would do without hesitation that choice!