The application is very lightweight. Check the Num Lock Holder process in Task Manager and you will find that the application still have 0 % of CPU usage even when you have not too much powerful processor (tested on Intel Core i3 CPU in laptop).
The aplication is minimized into System Tray (Notification Area) after start by default.
There are more methods how to detect Num Lock change and if the default method will not be suitable for you so you can change it any time.
You can pass arguments into CMD parameters and overwrite any saved or not yet saved configuration setting option.