It's along the same lines, but an NSL can be challenged in court (the FISC is a secret and lopsided court, alas). Companies like Apple and Google have fought specific orders publicly (and possibly some secretly), and some have won.

NSLs are also narrow in scope: they compel data disclosure, not active technical assistance in building surveillance systems like the Chinese law.

The Chinese laws can compel any citizen anywhere in the world to perform work on supporting state military and intelligence capabilities with no recourse. There have been no cases of companies or individuals fighting those orders.

Not at all. If you're an employee at a company that receives a National Security Letter then you can just quit if you want to. Unlike in China, the US government can't force you to keep working there to suit their purposes.