Don't get me wrong. SimpleR State is a "complete" library despite the simple API. It supports things like selectors, async actions, and plug-ins. And soon, it will come with built-in plug-ins like persistence, Dev Tools, validation, etc.
Everyone has different priorities when choosing a library, so I suggest going through the design goals that I highlighted in the README file, or complete documentation here:
and see if it fits what you're specifically looking for in a library.
At the end of the day, all these libraries are just React code. In that sense they differ in terms of patterns/principles behind their implementation, but maybe more importantly, in the API/syntax (which is what immediately matters to the developer using it). This is what I can confidently say that SimpleR State delivers... one of the simplest APIs you can find.