In any case, I'm not sure that any of the protections apply to foreigners (the criticism is all about how they might accidentally target Americans) so for those who are neither Chinese nor American citizens, it makes no difference. I would be happy to be completely wrong about this if you have information about how foreign citizens' rights are protected from US intelligence gathering.
The NSLs were merely meant as an example to show how US companies can also be compelled to assist in their government's intelligence gathering. You're right that they can (in theory?) challenge the secrecy part specifically.