1-According to Dan Abramov, form state is inherently ephemeral and local, so tracking it in Redux (or any kind of Flux library) is unnecessary
2-Redux-Form calls your entire top-level Redux reducer multiple times ON EVERY SINGLE KEYSTROKE. This is fine for small apps, but as your Redux app grows, input latency will continue to increase if you use Redux-Form.
3-Redux-Form is 22.5 kB minified gzipped (Formik is 12.7 kB) My goal with Formik was to create a scalable, performant, form helper with a minimal API that does the really really annoying stuff, and leaves the rest up to you.