I've tried flow too. I've got an article on the boil that walks through creating a production ready SPA with Babel, Typescript, and Flow. Covering the whole stack including Webpack, unit tests, and integrating Typescript with Babel (which is still a must as far as I'm concerned).

If I got to make a choice, I'd use tern.

Except it is impossible to prevent it from typechecking node_modules; so if you have a dependency that was checked with a different version of flow than you are using, you may see errors that are impossible to silence.

The only way I've been able to get Flow to be usable on my low-specced laptop is to tell it to [ignore] node_modules/.* and add a file to both [ignore] and [libs] which has one of these for each of my dependencies:

    declare module 'npm-module-name' {  declare var exports: any;  }

I needed similar for TypeScript when trying to use noImplicitAny: false - adding "typeRoots": ["node_modules/@types"] in compilerOptions and a d.ts file with the following listed in "files":

    declare module "*"

Typechecking third-party dependencies seems to be a bit of a crapshoot if you're not in a part of the module ecosystem where the tool you're using is either quasi-required, popular or has module authors using the same tool and shipping type definitions themselves. I've had contributed type definitions in both Flow and TypeScript "break" working, tested code.

Typescript is different - I can use type definitions from NPM without typechecking dependencies I don't import.