easiest way to get up and running w/value in the nix ecosystem is https://devenv.sh and as time goes on use escape hatches to utilise more of nix ala https://nix.dev
There are things it does that are very helpful, like enabling a PostgreSQL server without much setup, but other things like forcing certain language toolsets goes a bit too far—especially when those tools are already in Nixpkgs and setting up a base devShell provisioned with a few console tools is one of the easiest things to do with Nix the language already.
getting an entire team or project up and running in less than 5 mins with devenv is a fanstastic introduction for folks who do not have experience with nix. devenv solves the “onboarding new developer in a couple seconds without having to learn nix” pain point.
the next step there is to migrate away from only using nix shell (via devenv) and go for making ci reproducible locally once folks are more comfortable with nix/less career risk for introducing new tech.
then the world is your oyster.
use build2dockerImage and start creating docker images that are reproducible and use them in production.
The world is your oyster approach is skipping Docker and just running Nix on the server without the overhead of containers.
fwiw, NixOS does not support reproducible builds as defined by the Reproducible Builds project. They support reproducible environments/configuration/deployments or how you want to describe it.
see also https://reproducible.nixos.org/
It still amounts to less testing then what distros like Guix, Debian and Arch Linux is currently doing.