direnv is small enough that you can manually audit it by reading the source code. nix-direnv is also small enough for this, and conceptually it is a replacement for direnv’s builtin Nix support.

You don’t need home-manager yet, and you can put it off for a while; it’s mostly useful if you want to instantiate a homedir on multiple machines.

It must be nice to have never productionized a prototype; meanwhile, in the land of startups, putting experiments into production is standard operating procedure, despite being a bad idea.

The more important part is that flakes are unstable. The concept is solid and clearly works at scale, but the precise API available to users is not yet finalized or versioned.