Great deal for the 10 bucks

I use it on ipad. This app performs as good as 100 bucks quality tuner if you want to quickly and accurately tune guitars. If I tune guitar with polytune and then check with the reliable ot120 orchestral tuner it is spot on and so it is if I do it the other way. That means the accuracy is the same or better, about +/-1 cent.
For other plucked or hammered instruments polytune often works pretty well, I tried harp and it worked flawlesly across the range (in fact I found it to be a bit more sensitive for low strings than the orchestral tuner that may have problem with the longest quieter strings), dulcimer is also pretty reliable to tune with polytune which is a surprise (for example you will have hard time to tune dulcimer with a strobo tuner or normal guitar tuner). Violin is a bit more problematic when plucking with polytune as the note will jump to wrong one because it seems too quiet for the ipad mic to register. Bowing is ok.

The polyphonic tuning for guitars actually works and it is very reliable! It is a bit amazing piece of alghorythm as this was impossible just few years ago. If you need tuner for home and have iphone or ipad, you cant beat the price on this one.

Oscar Ottawa about PolyTune