It abstracts Nix in a way you don't have to know or learn anything about the Nix language.
I wrote a few words on how I use it instead of Homebrew [1].
[1] https://mootoday.com/blog/i-replaced-homebrew-with-devbox
More accurately, when you use a package manager, you use the “ecosystem” including the package index and pre-built binaries, and the cli. There aren’t many alternatives to homebrew as an ecosystem, especially including cask. Macports isn’t a homebrew replacement in the sense that it doesn’t have “cask”. Nix has something similar, although not as many packages. This makes nix probably the only viable alternative to homebrew with cask.
But nix is very hard to onboard. Devbox just makes it much easier to start using in say the first 30 min.
Now I have one tool to manage all dependencies.
Other than that, it likely comes down to personal preference.
One neat thing is `devbox global push/pull <repo>` to persist my config in a repo.
It's very lightweight and gets very powerful combined with `git worktree` to work on multiple branches in parallel, each with its own database instance.