I don't get it, they've nominated face to face basically every week anyway so that's no different, and with the extra benefit of immunity and keeping the prize fund nice and high? I'd be charging towards that button the second I could.
Why would any of them be scared to press the button? Unless I've misinterpreted the twist and the actual 'underlying theme' behind it is 'who can get immunity first?' rather than 'will they dare press the big scary red button?'.