The main advantage of NixOS containers, to my limited understanding, is that since they are built by Nix, all dependencies are updated with nixpkgs (no woefully out of date stuff in one of the layers of the container image) and you can pin these if you need to.

I’d like to understand the differences and similarities between the two better too though.

I think they know. I think we are realising these people are eugenicists.