Nix Flakes are stable enough to replace nix-shell and lets you pin versions, so it has a significant reliability advantage.
Things get a bit tricker when flakes are paired with home-manager and especially nix-darwin, as the error handling leaves a lot to be desired (opaque errors that are extremely difficult to debug, leaving you with few choices outside of nuking all nix and re-starting).
Things get a bit tricker when flakes are paired with home-manager and especially nix-darwin, as the error handling leaves a lot to be desired (opaque errors that are extremely difficult to debug, leaving you with few choices outside of nuking all nix and re-starting).