Functional prototypes > Polished mocks. In the early stages of exploring a new product idea, the feedback you get from people actively interacting with your thing is so much more valuable and insightful than if you simply described it and showed some UI screens. As someone actively playing with several new prototypes, it's been so amazing actually being able to use something to give candid and direct feedback based on what I'm experiencing, rather than just hypotheticals on what I think I'd…