NixOS has much more packages, and they are more up to date. Honestly, it is a shame because there are many things about Guix I prefer (especially its license). Also, if you are a developer, it is really nice getting to use nix flakes to set up your development environments.
There certainly are very useful applications for IoT. For example, at my house it regulates heating. It probably saved like 30% on my heating, with the added bonus that every room is the exact temperature I want. Of course, this is all done locally on Home Assistant. If I can at all avoid it, I don’t want any IoT device that connects to someone else’s cloud.