There's nothing wrong with a 5.56 AK that came like that from the factory, I've owned several from different countries; Yugoslavia, Bulgarian, Polish. They were all fine.
That being said, Jim Fuller and Rifle Dynamic are a boutique custom shop. They do *not* manufacture rifles, they modify them. Of course shit stands a chance of fucking up with you force a rifle to do something it wasn't designed for.
EDIT:
I just want to make a further point that all those AKs I've mentioned, and even Russia's 5.56 AKs are all military issue as well. We can joke all we want about dumb Slavs, etc but the fact of the matter is these countries would not be issuing those weapons if they didn't work. There's a whole line of Yugo 5.56 AKs just for NATO compliance. Russia has even fielded the AK-101 with their military before and the new AK-19 just debuted as well. The idea that these weapons are somehow unsafe is ludicrous. The Bulgarian SLR-106 has always been a somewhat popular rifle in AK circles as well, and those are usually what the boutique shops fuck with when they get the idea that AKs should cost $1200. Have their been issues with 106s? Yeah, sure, there have been with every AK, but none of them has ever been magical primer strikes to my autistic knowledge. Now if you wanna talk US made AKs... Whole laundry list of fuck ups with those.