Anyone uses Nixpak?

I was looking at ryan4yin's new NixOS book and stumbled upon nixpak, a neat project that , as far as I understand, acts like a sandbox for Nix packages, similar to Flatpak. I've been wanting to try using it for myself, but haven't found any dotfiles I could steal from use as a references. If anyone uses this, I'd love to hear how, and what your experiences are with it.