I've tried many products on the in this realm of audio plugins and out of all of them PhraseBox was the easiest to setup, play with and understand. I was able to get going with most of its features in under 10 minutes:
Its easy: PhraseBox doesn't require you to learn a new mental model for abstracting musical notes and harmony. You put your chords in your daw, and you add or remove notes in Phrasebox, much like you would in your DAW's piano roll. If you know how to write chords and use a piano roll, you know how to use PhraseBox.
Contrast this with a product like Cognitone's Harmony Navigator and Synfire. In order to be productive, you're going to have to install multiple pieces of software, route your audio and then learn an entirely new mental modal for music composition.
Its not a limited or a toy: PhraseBox doesn't try to replace your own creativity, it assists in getting you "in the zone" faster so you can start creating. PhraseBox isn't a "Black Box", its more like simple way of using a piano roll for sketching melodies / phrases.
Contrast this with some products which say they will compose your the music for you but end up generating cliche garbage.
Couple of things I would like to see in future releases:
Ability to select a group of notes and copy / move them inside the piano roll.