Congrats on a really nice review. I really like this lens (I have the Pro-Optic variety) and you cannot beat it for the price.
I would like to comment on one thing you mentioned, the build quality. Having dropped and broken and tried to repair one of these, they are not as "robust" as they feel. Some of the parts that move the diaphragm a relatively flimsy and easily bent. And the ring holding these parts in place are "spot glued" and made out of plastic. The result is that if they ever come apart, you will not get them to function properly again. Struggling with glue and shims can get it back together, but the diaphragm function will never be right once the flimsy plastic breaks or the metal parts get bent. At the price of the lens, it is not worth a "professional" repair.
However, my solution was simple. I could not wait to get another one and replaced this with a duplicate Pro-Optic version of the Samyang. I just tell myself never to drop it again!
Bottom line is that I would recommend this lens to anyone looking for a 14mm that does not break the bank, and in fact, can exceed the IQ found in some much more expensive wide angles out there.
Thank you for this "real life" observation. This is the kind of thing that most reviewers (like myself) wouldn't know unless something similar happened. We judge a lens by feel and the apparent quality of the moving parts, but don't necessarily know the internal construction or how it would react to a bit of "violence".
The fact that you replaced it with a second copy also says something significant!