While I like the idea and the execution overall, there are too many elements that cannot be changed in the "free" version to make it even remotely useful. I mean, really: can't even change the button text?
As a practical matter, too many restrictions make this not "free" software at all, but merely a demo for the paid version. As it stands it is completely unusable unless you want a slight variation of one of the 50 pre-designed buttons. And that variation does not even include your own button text.
Overall, I rate it: not only is it not useful, it is actually unusable.