We've been using feature flags but mostly for controlling when things get released. But feature flags carry their own issues, they complicate the code, introduce parallel code paths, and if not maintained properly it gets difficult to introduce new features and have everything working together seamlessly. Usually you want to remove the flag soon after release, otherwise it festers. The production branch is also ok, but committing out of order can break references if commits are not in the same order as master, and patching something directly to prod can cause issues with promoting changes from master to prod, it requires some foresight to not break builds.