The technologies develoved by a successful Iron Drome in israel, and regretfully tested in real life by rockets being fired by militants into Israeli population centers, will then be shared with the US, who can use this at will to make US Iron Drome defense systems in order to protect US interests directly (e.g. US military bases in war zones and strategically important sites within the USA). I think that the US is genuinely interested in aiding the defense of Israel, which we are thankful for, but there are additional US interests at stake here, that have nothing to do with Israel.
Key U.S. House Democrat cites troublesome issues in Iran nuclear deal (Reuters)
from the article: U.S. Congress gives Obama okay to fund Israel rocket defense