That certainly looks less trivial than writing it directly in your .gitconfig file.
It's the same condition and setting as what's in the article, but now with a build/templating stage and a new programming language to learn with unusual syntax.
Agree on your comment re build/templating and new language. Nix is weird and NixOS is complicated. Nonetheless I have convinced myself that I like it.
In TFA the author must set up two configurations: the .gitconfig, and the file which is included in the .gitconfig. Home-manager does this automatically through one config parameter. That is what I was pleased with and wanted to share.