Nix comes with some friction since its approach to packaging is so different. When you start using it, 95% of the time it's great. But because Nix does things in such a different way that it can be difficult how to navigate that last 5%.

In terms of installing packages, it's an advantage to Nix that it works with both macOS and Linux. While not every package is as cross-platform as it could be (e.g. some desktop apps that are available on both are only packaged on Linux), it does mean it's easy to use e.g. the same version on Tmux in all computers you have access to.

Nix can be used for more than installing packages. e.g. the nix-shell allows for dropping into a shell with particular programs installed.. like a generalisation of rvm/nvm/whatever. Nix can be used to describe Docker images instead of using Dockerfile. NixOS uses Nix to describe its OS's configuration and services, rather than just packages. (Whole OS setup described from a single file is pretty neat).