I created an account and found the one possible reason to go for a subscription:
If the song you want to chordify does not exist already on the public platforms. But you gotta find such a song first if it’s a song that was published by a label.
As free user you can’t upload stuff so you have to take what is on yt, spotify and such.
Edit:
I tested it on one of my favorite songs. It has written out the chords fine but… couldn’t they have coded it to not have the same letter in the progression?
It’s Bb A and not A# A. At first I thought it was wrong but then I realized it’s the same tone but the notation is dodgy at least.