I had already been using the excellent full size Polytune for about a year and was extremely happy with it - however the chance to locate a little real estate on my board was hard to resist and this little wonder is just as great as it's bigger brother.
The Tuner can be used in two ways - play a note and it will tell you visually what the nearest note is and you can easily tune pitch to that note.
However play all notes open and it quickly tells you which notes are out of tune to your reference tuning which is default EADGBE but using the botton on the side can be amended to a variety of different weird and wonderful tunings which is handy for me being in a band with drop tuning (yeah yeah the singers knocking on a bit). Typical well built construction from TC and ideal for pedal boards.
No space for a battery with this little baby (unlike its bigger brother) so best for boards unless you want to carry a power supply as well (not supplied).