I don’t know the hit/miss ratios but their ‘Iron Dome’ system seems to work quite well. Seems this defense system is being put to the test nowadays. I don’t see how an attack on Iran goes without casualties in Israel, however.
One way or another, there will be casualties in Israel. Whether it is from terrorists in Lebanon/Syria/Egypt timing the attacks they would have launched anyways and claiming they are retaliating for IAF taking out the Iranian nuclear weapons program, or from an Iranian nuclear weapon, there will be casualties. While I detest both options, I see only one of those choices as morally acceptable.