I can sort of comment on this since I've used Flask-RESTful and Django REST Framework where a lot of the Flask-API design is/will be borrowed from. I think the browsable API feature is great but it's not the killer feature for me. To me the killer feature is the well-designed serialization and validation architecture. In Flask-RESTful this seems half-baked - there is no notion of hyperlinked references or nested objects. At our company we ended up implementing our own serialization & validation layer which felt a lot like reinventing the wheel. My hope is that we can bring this same great architecture over from DRF to Flask-API.