I've been using Atomic stuff for a while. First Silverblue but now I use Bazzite Gnome.
I actually use Nix ontop of it for dev tools and CLI tools that Flatpak doesn't handle.
I don't like the toolbox style of doing things. Nor devbox, dev containers, nix shells, whatever. Too much hassle.
But I do like using Nix + Home-manager to manage my home directory and tools, especially between computers as it's all in a git repo and has separate configs.
Just look up Kindle DeDRM, it is easy enough to remove that stuff and then even convert them to epub