There is only one way to know if these things work, and that is to give Hamas permission to do their own test with Qassam rockets. Somehow, I don't think that will happen. Aside from the cost, estimated at one million per missile, it would be shattering blow to the credibility of the Israeli military if it failed to knock down the Qassams.
Palestinian reportedly shot dead by Israeli soldiers after approaching Gaza border fence (Haaretz)
from the article: Iron Dome missile defense system to become operational within weeks