"They look OK"?
Look what is listed in the ad: Professional Supplier-Hong Kong.
This is a knock-off of an ARMS mount.
I wonder how many reports of "I broke the lever on my ARMS mount," is from someone unknowingly using commie-chinese junk copies of US products?
I have been using ARMS mounts for over 20 years (that I know were U.S. made under license from ARMS) and have never had one break.
I believe this Hong Kong crap is the answer.
They are probably both MIM parts, probably both made in the same outsourced shop, from the same pot metal.