Here's some good posts about submodules and alternatives, so you can make up your own mind:

http://blogs.atlassian.com/2013/05/alternatives-to-git-submo...

https://codingkilledthecat.wordpress.com/2012/04/28/why-your...

From what I've gathered skimming the numerous blog posts venting about submodules, it seems that people have trouble with submodules because they are trying to integrate them into a workflow they work poorly in (i.e., rapidly changing modules). There seems to be room for improvement for that type of usage, given what people are saying, but I wonder if there have been any changes to submodules since those posts (many of them are dated around 2011-2012).

My own positive experience with submodules involves dependencies that only occasionally change; I can always point to a specific tag that should be used.

Yes.

One should avoid to extract a component from the repo as a submodule too early, i.e when the interface of the component is not mostly stabilized.

If each commit in your "main" module is paired with a commit in your submodules, then you might be missing the point of module separation.

Even if the interface is stabilized, when you update implementation of a submodule you will still have to recursively update all submodules from main down to the changed module.

How do you point to a specific tag? Do you set branch : (tag)?