> Any sales to US firms could be curtailed or punished.

That doesn't really restrict the NSA, CIA, FBI or any other agency/PD from buying their services. After all, that's what "black budgets" are for.

Most of these firms use private contractors to do the dirty work. Unless contractors can bypass legal oversight, they'll be constrained as well.

Overseas contractor hired by a shell corporation gets the phone sent outside of the US. Boom.

All this assuming they even care about legal compliance, which I am sure that under the correct circumstances it won't matter one bit.