Earlier quoted context omitted.
While $1 is certainly far less than the value this app provides, it’s going to be a hard sell when there are several free apps which do the same thing.
Or if you’re paying, just spend the extra few books (it’s $10) and get Petersen Strobosoft which is the absolute gold standard.
Plus, it's much less fiddly to handle than balancing a phone and a guitar :)
Ultimately, it's a matter of taste, and what you use them for.