Also, I think it's harder to customize things. I choose Vaadin for a reason, not having to learn or deal with frontend stuff. But I find myself trying to fix my UI a lot more than developing the backend. I used to work with Thymeleaf before, so I had to do all the work, import webjars with components I wanted, dealing with Bootstrap, etc... The reason I went Vaadin was to bypass all that. But right now I feel I can't make a UI look like I want or be more responsive.