Against Russia or China, this kind of a system is worthless. I believe that the contractor is selling this as deterrent against Iran or North Korea.
... And even then it's worthless, because if either wanted to nuke the US, they wouldn't launch it on a missile, they'd pack it on a ship and sail it to New York.
From a certain perspective, it is actually good that this is worthless against China or Russia: namely, if they don't perceive it as a threat, then they won't fight its deployment or try to build up arms in response.
Consequently, it may prove useful in neutralizing the threat posed by medium-to-long-range weapons possessed by particular actors (Iran, North Korea) to allies in the region. (I say allies because I agree with you - if they wanted to attack the US, doing so via conventional means would be extraordinarily foolish.)
... And even then it's worthless, because if either wanted to nuke the US, they wouldn't launch it on a missile, they'd pack it on a ship and sail it to New York.