This is a simple button for Sonoff Basic to be able to switch it by foot. It will operate on top of the tiny built-in button. It has a small hole for the built-in button, so you should not be able to break the built-in button even if smashing hard the foot button (theoretically designed, not tested hard, and this may depend on your print, so keep it gentle :-)) The space between the foot button and the sonoff should be enough to allow a smooth slide between the two.