I haven't used devenv or devbox, I've taken the full Nix/NixOS plunge - sorry I can't be more helpful! I've just seen devenv on HN and glanced over its homepage and saw that it was based on Nix but supposed to be easier to use. If you want to jump straight to Nix itself, more power to you! There's a big learning curve, but I have found it very worth it.