Thank you Sarah for featuring this plugin here!

We wanted to make this as easy as possible and this is still a work in progress.
The plugin itself is functional and easy to use, any bugfixes and commits are welcomed on its github repository on https://github.com/aristath/kirki (there's a known bug on the "required" argument, currently it only works with buttonsets but will hopefully be extended soon enough).

As for the Shoestrap theme mentioned above, it uses exclusively the customizer and is currently under construction. By that I mean that we've added all the options to the customizer and have started working on their implementation but some of them are not yet implemented in the theme.
Just a heads up... it's not bugs, it's just unfinished business. :) Just like on the kirki plugin, you can contribute to this theme on it github repository.