My use case is simple: I wanted a simple, stand-alone GUI-only app for developing my static HTML website for Neocities. To that end: This app does the job well enough, once you get used to it. And in my opinion, the devs should consider remarketing the app towards that demographic instead of as a "*epub* visual XHTML editor," otherwise you'll just get confused people like the guy who commented before me. For those actually looking to develop an ebook: LibreOffice, OnlyOffice, or perhaps what this project was split from Sigil would be your best bet, though I can only vouch personally for LibreOffice
As far as I can tell, this application has absolutely no functionality for anyone who needs to edit an ebook.