It is mostly from external observation. He seems to be the reason that bcachefs isn't being shipped in production today, as he is trying to work through all of his backlog rather than shipping it in a WIP state. This is very different than how developers of a certain filesystem in Linux's kernel source tree that I shall not name do things. If I recall correclty, a developer of that filesystem told me several years ago that if they did not ship the code for users to use it, they would not find bugs. That file system is not much less buggy today than it was back then. :/