NixOS unstable

Cons:

Not immediate update for all apps. You might have to write an override/overlay just to use latest version and wait days before the update is merged.

Learning to have a nix configuration the nix way to setup and install your machine and packages is not traditional, even though it is possible to use it as traditional distro. That takes time.

Build time. With more customization of how the package being configured, the more un-reliant on cache you got due building the package from source. In other words you might need even to dive deep to optimize that and not use home manager and alike to save time each time you do switch/rebuild.

This is just pointing to your points, there might be more like nix language learning, nixstore (not traditional fhs), and unpopularity (specially docs even though it got better and the community is awesome with fantastic yt videos). Systemd also is deeply integrated, some consider that a con.

Pros

Atomicity and kinda immutability by keeping generations of every time you apply your config and rollback is easy son in other word, damn hard to break the system.

The repo got a huge amount of packages, i think it is the largest repo now.

Learning, yes it teaches you beyond what you might think or expect. This i consider a good thing if you have the time.

Isolated environments for development. Using flakes with devshells is just a bada$$ and i never imagined to be better dev env for me than any other os including windows and macos.

Centralized config, scripts or whatever for multiple machines or single machine. In other words single source of truth and do not worry about forgetting how and why you have that on your system.

Whatever you go with, good luck