Right now I have a VM running NixOS, so I can figure things out. What annoys me is that when asked to list all the programs I want to use, I struggle, but installing things on the fly is so much more easier. Nix-env does that, but it doesn't add it to a /etc/nixos/configuration.nix, does it? Also, I know about home-manager, but I've heard it's extrememly difficult.
No, nix-env installs to your user environment, which the nixos-rebuild command barely touches. It doesn't touch the global configuration file. In fact you can even manage user accounts imperatively.
My approach is the following: try a program using nix run (or nix-shell, depending on the case) and if it does what I want, add it to my configuration and nixos-rebuild test. It will then be available permanently on next update.
What I also do is keep all nix-related files in a git repository under main user control and have the flake.nix (if using flakes, otherwise configuration.nix) soft linked into /etc/nixos. This also enables rollback on your configuration, not only on the actual system state.
I agree that each package takes more time, but OTOH, you save a lot of time and effort in the longer run. Also I don't really have that high fluctuation of packages that it actually matters.
home-manager is a bit in a weird spot in my opinion as in it's not very clear how it should be installed. If it's a NixOS module, your changes will only be applied during rebuild - which only root can trigger. But if you're already triggering those as root, you might as well as the packages globally. I generally install globally and configure the options using home-manager.
Alright, if that's too much of a hassle you shouldn't switch. I'm unaware how to do all of that in one step on the command line. All I can say is that the last time I added programs to the array was two weeks ago. So the workload is negligible… on the other hand, on Arch, when installing something new that you then decide not to keep, you need to track the dependencies that you no longer need (pacman -Rs $(pacman -Qqdt)) if I'm not mistaken.
Also, the amount of work saved depends on what you're installing: let's say you install OpenSSH on your machine. On NixOS, that's editing about six lines in my configuration and then rebuilding. On Arch, that's
installing OpenSSH (pacman -S openssh)
Editing /etc/ssh/sshd_config
Editing your firewall settings (This happens automatically on NixOS)
Enabling and starting the OpenSSH service (NixOS does this for you)
Applying your changed firewall rules (again, automatically on NixOS and guaranteed to be correct)
So you have double the configuration files to be edited and triple the commands to be ran, while during all of this, nix actually does the thinking for you (e.g. you change a port in your OpenSSH config -> the firewall configuration is updated automatically).
Sounds neat. I am really considering NixOS, that's why I'm asking for advice here. It really sounds like a nice and more convenient distro. Sadly, I still haven't figured out how to make my own builders, even after Nix Pills. Thankfully, programs like crate2nix exist.