How it works is pretty simple.
You create a read-only Stripe API key (this key stays on your laptop), the widget gets the last 3 months of your revenue to calculate an average, and then you can specify your monthly expenses and adjust a tax and buffer %.
Then you get a nice card that shows you how much you can pay yourself this month.
It's fully open source under an MIT license. Please let me know if you have any feedback, and feel free to submit a PR.