JS with flow is way better than JS without flow. It prevents a whole class of errors, and you can basically opt-in and opt-out of the type system at any time if you're having trouble with it too. I wrote a blog post about it a while back: https://www.aria.ai/blog/posts/why-use-flow.html

That being said, while I started out using Flow, TypeScript just has way more community adoption and better tooling. So at this point, I usually recommend TS over Flow to most people. But using either of them is way better than writing just regular JS code.