Why is this better than Orgmode? Orgmode is human readable, opens in any text editor, handles everything from bullet points to tables, and Github even has a Markdown-like renderer for Orgmode files.
The obvious advantage is that all platforms share the same code. As such it's easier to add new features. While for org mode emacs, orgzly, etc are separate projects that have to be kept in sync
The more likely pain-point is that on one device you have extra tools/configuration set up (e.g., org-latex), but these tools aren't available elsewhere (such as in orgzly). But I assume that this is a given for orgzly users: they probably don't expect they can do everything that org-mode enables in Emacs (like producing PDFs via LaTeX). They just want to do basic edits, and don't want to lose data when the document round-trips between Emacs and orgzly. (I don't use orgzly, but I assume that safe round-tripping is a feature...)