[pxc]

Flakes and the unstable branch of NixOS (the `nixos-unstable` branch of Nixpkgs) are unrelated.

Flakes is an "experimental feature" of Nix itself, but it has shipped in stable releases of Nix for years now. There was a time when you had to build an unreleased version of Nix to play with flakes but that was a long time ago.

Whether you use a rolling release for the package set, e.g., nixos-unstable or nixpkgs-unstable, is orthogonal to whether or not you use flakes.

Fwiw, I generally prefer to run the unstable branches of Nixpkgs. Occasionally you hit something you have an opportunity to fix yourself, but that's not very frequent these days, even on the unstable branches.