[ddevault]

No, I haven't run into any such issue, though I have only used it with small to medium sized repositories. The repo simply grows linearly with the size of the secondary repository. With a submodule, you would have to clone it just the same. In fact, you might enjoy some benefits from cross-compression by using subtrees that would not be available to submodules, and it's faster to reuse the same clone connection you were already getting the source from.