Fyi: NixOS would shine everytime a client handed you a laptop for the gig. Your working environment reproducible and declarative. Setup in minutes, not hours.
I would suggest Home Manager though, which will let you set up your environment just as well and is very portable, while still affording you a mainstream host system of the company's choice.
It would be interesting to be a fly on the wall and listen in when infosec calls you and asks why your laptop disappeared from their monitoring tools and you told them you installed nixos (assuming that would even be possible) because that's what you prefer.
In a similar sense, knowing how to work with the builtin tools of major OS is a huge advantage. If you can write your code in vim or nano or notepad without breaking a sweat over your favourite hotkeys not working, that's a lot of hours saved.
Often this is activation scripts, e.g. home-manager will complain at you if you are attempting to overwrite an existing file not managed with home-manager unless you tell it to forcibly overwrite the file.
You can get yourself into situations where even in NixOS land, switch-to-configuration will refuse to switch due to some kind of violation, e.g. a systemd mount service wholly failing. I've had an experience like that recently.
The Nix store is not a perfect get out of jail free card for this, everything impure must be wrangled by something eventually.
What I'm really trying to say is, the world is messy and full of impurity, it's unavoidable. The thing that manages Brew, casks and app store applications for you within nix-darwin is no different than home-manager managing home.files or switch-to-configuration acting upon systemd.