As a longtime superfan of the PolyTune pedal, I was shocked to discover that this plugin quietly existed in the world. I used to check on the TC website all the time, wondering why they hadn't released a plugin version of this revolutionary plugin, and then one day during some plugin research here—what do I find? A listing for PolyTune! And it's only $49.
So this functions and looks exactly like the guitar pedal. No surprises here. I noticed that the GUI is not Retina-ready, which leads me to believe this plugin might be somewhat neglected and may not get updated. But for now, it's working fine on MacOS Catalina, as of April 2021.
Generally, the polyphonic tuning is accurate, and can be very useful for dynamic sections of a song where the player is hitting the strings at hard levels and might be skewing the tuning. Using the polyphonic mode can get your a nice average tuning for chords, and then it will automatically switch to single-note mode when you hit individual strings. It's brilliant.
There is a very generous trial version available from the product page, I highly recommend any and all guitar players grab it. It makes life so much easier.