Originally posted by Jonathan Mac I think it's a clone of the mark II Canon one, which is probably the lens with the worst reputation for build quality ever. I have the STM and it's light but well built.
Sounds plausible - I've seen a couple of those broken too; one in a job lot I returned to the seller because everything was smashed (the idiot didn't put in any padding between the lenses), the other was on a camera body I didn't buy in a street market.
The Nikon version of the Yongnuo is actually pretty good mechanically, but it's a near clone of the early Nikon 50/1.8G lens (no on-lens aperture controls), and I have a 50/1.8D which is as good optically and has aperture controls, so again I didn't keep it.