One run per device. Run the script once on each device you want to use. Each device gets its own key; the VPS accepts all of them. For a new VPS, run it again with a new name and IP.
iOS has no full Bash terminal like Termux. Use a PC terminal for the first setup, or an iOS SSH app with its own key import. The alias itself lives in ~/.ssh/config on the terminal where you ran the script.