If you add one of these type checkers into your CI or a pre-commit hook, it provides the same guarantees you get from a compiler along with the same tooling benefits. It gives you the option of using the structure when you need it, but not being forced to use it when you want to take advantage of some of the more dynamic features of the language.
But none of the runtime benefits of having static types in the compiler, since the runtime still can't trust the types. Still, half a loaf is better than none.
