From the Israeli perspective, the fear is that if pressure is off of Iran, Israel would be left having to accept the balance of power in the region significantly shifting toward Iran. It's not an existential threat, but it would definitely be a problem for Israel.

There seems to be a consistency, in that people who have had access to the Iranian program - people who actually have had boots on the ground and have been able to investigate and inspect the program - have consistently been saying these things.

NIE presents a major obstacle to those who are pushing for military confrontation. In many ways it is a severe blow to their agenda. However, I wouldn't go as far as to say that the risk has been significantly reduced or eliminated.

Beyond that is the fear that the United States will end up negotiating and agreeing to a deal with Iran. The Israelis do not like that either because they fear the deal will come at the expense of Israel's security interests. From an Israeli perspective, the NIE makes the risk of some sort of settlement much greater.