I'm using it for a small-to-medium sized project, and the generated files aren't too bad to work with at that scale. The actual generation of the files is very awful for Python specifically, though, and I've had to write a script to bandaid fix them after they're generated. An issue has been open for this for years on the protobuf compiler repo, and it's basically a "wontfix" as Google doesn't need it fixed for their internal use. Which is... fine I guess.

The Go part I'm building has been much more solid in contrast.