BTW the “better option” here is nix run. nix-shell -p foo sets up the environment as it would for building foo, so all of foo’s dependencies are in your PATH and all of the other environment vars are set too (I count 23 env vars containing NIX), but nix run produces an environment much more similar to what you’d get if you simply installed the package (e.g. it basically just prefixes your PATH with the appropriate directories from the specified package).
That said, nix-shell replaces your normal shell initialization files and nix run doesn’t, so depending on how your .bashrc is set up you might override the PATH. For example with my setup, echo $PATH in a nix run shell starts the path with /usr/local/bin before the nix-provided path value, because my current .bashrc unconditionally prefixes my PATH (which I really should fix).