Pros: vertical tabs, web apps, side panel, workspaces, many customizations. to be clear tho, Firefox has already stated they will be incorporating most of these features by version 130 or sooner.
Cons: no mobile app, video playback with DRM may be an issue on some sites, uncertain future, essentially it's maintained by one dev so if they ever go the future is uncertain.
tl;dr, Floorp is kind of like Vivaldi with customizing and privacy in mind, but based on Firefox's gecko engine