Git submodules are only a viable tool for truly external dependencies that need to be built from source, in which case adding a submodule and special case for y

Git submodules are only a viable tool for truly external dependencies that need to be built from source, in which case adding a submodule and special case for your configure/make scripts is one of the easiest ways to add a dependency to your project. If you're using it for dependency management for internal projects you're going to have a bad time. Especially as things get more complex. The only advantage is if you need to keep particularly components open source. Otherwise just use a mono repo.