PieFed is odd in both having several features that Lemmy lacks - categories of communities, tags on posts, and most pertinent here, the ability to truly block all users from a specified instance without requiring admin approval (which neither Lemmy nor apparently Mbin offers) - while at the same time lacking in several fundamentals, e.g. user tagging such as @openstars@piefed.social generates no notifications, and the UI is highly difficult to work with for posts with many comments and especially deeper chains that are nested (there is no option to go one level up, the only choice is to start all over at the top level, at which point browser searching does not work when the comments are buried too deeply, as is our very conversation here).

Yes there is a request for a PieFed API. In the browser the display options are a List, a Tile, and a Wide Tile. Off the top of my head, Lemmy seems the most polished - e.g. there are many apps providing choices for how to access it - followed by Mbin and PieFed that each offer different feature sets.