This has been going on for years and is pretty well common knowledge in the commercial fishing retailers I've been to
All of the marine supply stores in my little town carry both real and what is referred to as "Chinese" shackles. They'll tell you the real ones will hold to their rated weight. If you ask about the Chinese ones they shrug and say, that's up to you.
If I care about what I'm connecting I always buy the genuine ones. I did buy some Chinese shackles to hang bird feeders. But, I've seen lots of people look at the load rating for the real shackles, then find the same size in the "Chinese" version (by size, not rating, they don't display load ratings on the Chinese shackles) and save themselves $4. Not worth it to me.