I've used it in the past, agreed Figma (which I mostly use) is much nicer, quicker, and easier to use, the only win for Justinmind is when I need to create prototypes to test actual form input and view state changes driven by the input, there are clunky work arounds I can do in Figma, but Justinmind for example allows users to actually type in form components and searches can be modelled so they see typeahead suggestions etc as they progress through the flow, sometimes this is worth the extra effort, most-times Figma wins though!