I built a small utility as well, and I'm using a somewhat unique payment model.
It's free and open-source on GitHub. You can download the source code and build it yourself with Xcode.
https://github.com/pkamb/powerkey
I also provide a $5 built app available to purchase via Gumroad, code-signed with my Apple developer account and ready for immediate use without Xcode with no scary macOS warnings:
https://gumroad.com/l/powerkey
I found that this model works really well for small projects where you want some of the benefits of open source and don't want to deal with upgrades or nag screens.
It would be even better if GitHub built some "paid release" features into their product, in addition to their Patreon-style Sponsors feature.