Note that a phone number can be spoofed, rendering a call-blocker rather useless.
For all intents and purposes, if they're spoofing known numbers, that would be an issue. But, if you don't recognize the number and you don't want to answer it, that's where the button would come in handy. Instead of answering then hanging up to stop the ringing, you could just press the button to zap it. That way, you can zap at the press of a button a phone call you don't want to answer and you have a 50/50 chance that a number you recognize is the actual owner of the number.Note that a phone number can be spoofed, rendering a call-blocker rather useless.