Very promising

I’m a user of Elementor, Beaver Builder, Oxygen, and a reluctant convert to Gutenberg after years of customizing the classic editor. ?? Zion Builder does a number of things very well (like clean code, parent/sibling selectors in hierarchy, and custom length units by default [e.g., easy to change “24px” to “2em”]). Both the free and pro versions are missing some crucial features (like menu elements and the ability to change responsive break points), but it’s early days yet; I expect those are coming. The developers will have to work very fast to get Zion up to speed before Full Site Editing becomes possible in Gutenberg, if they want to capture a significant market share, I think.

In addition to above, star rating reflects: using id’s to style elements (classes are considered a best-practices), lack of ?-Z undo, incomplete history (does not track, for example, adding an icon to a button), lack of focus styles and ease of adding :hover, :focus together (basic accessibility is NOT a “Pro” feature!), and for putting the edit icon the furthest from the toolbox toggle. Also needs page/post/cpt search in link fields. Also suggested is putting an outline around the element currently being edited. When items are similar, it’s not always clear that you have successfully switched elements for editing (buttons, for example).