As matters stand presently, it would not be in Iran's interest to use NNEMP weapons. This is because Israel could mount a higher level EMP (an NEMP) retaliation. In strategic terms, therefore, Israel is in a clear position for "escalation dominance" because Iran is still pre-nuclear.
If the NNEMP weapon were used against Israel by Hezbollah rather than by Iran directly, Israel's "escalation dominance" advantage could prove less important as a deterrent, but it would simultaenously give Israel a carte blanche in destroying Hezbollah.
They know that.
In world politics, it would first seem obvious that sanity is better than madness. Upon reflection, however, the risks of a nuclear or EMP war could be as high or higher among “sane” adversaries. For Israel, a country smaller than America’s Lake Michigan, any failure to understand such a counter-intuitive assessment could hasten the onset of unprecedented hostilities with Iran. Most ominously, over time, this could mean suffering Iranian nuclear attack.
For Jerusalem, there are variously pertinent specifics. Contrary to conventional wisdom, Israel’s “Iran nuclear problem” is not principally about enemy leaders who could become “mad.” The more worrisome existential problem for Israel is sane and rational enemies who could become subject to decisional miscalculation, incorrect reasoning or mechanical/electrical/computer malfunction. Other nuclear hazards that could coincide with Iranian sanity and rationality include accidental firing, unauthorized launch and coup d’état. Israel National News - Arutz Sheva