Every pedalboard should have a tuner, and for the price, you can't really go wrong with this one. It's accurate and fast, and has a bright display. I will start with a list of pros and cons, with more details provided below.
* Small footprint
* Choice of chromatic and strobe tuner display
* Multi-string tuning
* Built-in buffer (can be switched off)
* Cannot change LED colours; keep this in mind if you are red-green colour blind(!)
* Only tunes to standard concert pitch (A440)
* Polyphonic mode does not support 7-strings
Accurate and fast
The Polytune tunes quickly and accurately. By default, the display shows a chromatic tuner, but it can also be set to a strobe-like display. The latter appears to provide somewhat more accurate results due to the higher precision of that display mode.
Note that despite being a chromatic tuner, the Polytune only seems to work with the standard concert pitch of A440hz. I could not find a way to change this calibration.
The Polytune can also tune all strings at the same time. This mode is not as accurate as single-string tuning, but the best part is that the tuner switches between multi-string tuning and individual strings without any buttons. So, for me, the polyphonic mode is mainly to check which strings need tuning: simply hit all strings to see which of them are flat/sharp, and then tune those one by one. It saves you going through all six.
Do note that I wrote ‘six’ very specifically. This mode only seems to support regular six strings, because it only shows six sets of LEDs. So if you have a guitar with seven strings, you will not be able to fully use this multi-tune mode. However, that doesn’t make this tuner completely useless for those guitars: the chromatic tuner does seem to accurately pick up the low B.
The display is definitely bright enough for most cases, though I haven't tested in outdoor situations. This mainly goes for the chromatic mode; when it comes to the strobe, I am not entirely convinced that this will be easy to see in the brightest surroundings.
Perhaps my biggest point of criticism is that the colours of the display cannot be changed. As a colour blind person, I have some difficulty with the red-green LED combination. The option to change either of these to, say, blue would’ve been helpful.
In addition to a great tuner, the small enclosure also houses a buffer. When enabled, the buffer allows you to operate the tuner in always-on mode. One reason for me to choose the Polytune 3 mini is the fact that the on/off switch is located on the outside of the pedal whereas the regular Polytune 3 requires you to unscrew the backplate.