I'm no Intelligence expert and I understand their thinking to deal with this threat before it becomes much bigger but I disagree with this approach. Bear with me, as I approach both positions. I personally think this approach hurts Israel more than it helps them. If it was in retaliation for a specific attack by Iran, maybe it can be justified, but not just the aggressor. They've done this before years ago. Did it work then? I don't know. Who knows?
These types of attacks should only be used against someone who is personally involved in murdering your citizens, not a guy, often forced by government; to work on their governments ambitions. That had always been Israels position, before these nuclear ambitions, which seemed to have forced their hand.
First, say what you want about a man doing what he does for his country, but, he's just an employee. Some schlep hired by the government to help them. He isn't the decision maker, so you are just bombing regular citizens who are now martyred, even if he didn't want to be. He will be replaced by others and you buy, what, three months time?
Second, and this is a big deal, it allows the Iranian government to have more support for a hardline approach to enemies and ensures citizens rally around them. Even those who despise the Iranian government now feel an internal desire to assist them due to a foreign power murdering a citizen on their soil.
This cannot be overstated. It was the same issue with Palestinians who bombed an Israeli cafe years ago. One of the women they killed was actually an Israeli woman involved in a group seeking peace. That group, surely didn't have a stomach for such a position afterwards. Israel responded aggressively time and again by bombing terrorists, so, it hurt the terrorists and their cause far more than it hurt Israel.
Third, it provides the argument for their enemies to side with nations like China and to justify their own activities. I have little love lost for the Iranian government, but in the long run, I don't see how this hurts the Iranian government long term. They will retaliate, and we won't know about it. When you lose the higher ground you can rarely recover it.
From a practical standpoint, this attack was probably in the works for some time in the event Trump lost the election. Once Trump lost, Israel acted quickly. If Trump had clearly won, I wonder if they wouldn't have just allowed the U.S to apply pressure through Trump to bring Iran to the table for a more solid, secure deal for the region and world.
Israel has been quite clear, they simply do not want to deal with Iran under the old U.S/Iran nuclear terms. They have always told the world, "we will defend ourselves any way we deem necessary" and they have been outspoken about their dislike for the Iranian Nuclear Deal.
In fairness, we don't live in their neighbourhood, so we don't directly feel the impact of such a deal. I often wonder if the China alliance and some in the West willing to bend for the Communists hasn't clouded the judgement of negotiating with Iran from a position of weakness, even meekness. Maybe a more secure, reliable and enforceable deal could have avoided this. This might be a precursor of many such activities to come in the next few years.