Submodule versus subtree merging
There is no easy answer to the question of whether or not to use submodules or subtree merging for a project. When choosing submodules, a lot of extra pressure is put on the developers working on the project, as they need to make sure they keep the submodules and the super project in sync. When choosing to add a project by subtree merging, little to no extra complexity is added for developers. The repository maintainer, however, needs to make sure the subproject is up-to-date and that commits are added back to the subproject. Both methods work and are in use, and it is probably just a matter of getting used to either method. A completely different solution is to use the build system of the super project to fetch the necessary dependencies, as for example, Maven orGradle does.
