The UI looks a bit outdated, it gives me vibes of some old software from 2000s somehow (probably because of the Java). And it would be really helpful to clearly state benefits of using Milkman instead of Postman right on the home page (e.g. performance benchmarks, UX, extendability, etc.). I see that it has some users and 1.3k stars so there're definitely some cool things in Milkman, probably you could just present them better