The FNS has drop safety issues and there is at least one that went off in a duty holster when a Maryland Officer bumped a steel door frame entering a police facility. Security video confirmed the officer had a box in both hands at the time of the (actual) AD. But that was not a QC issue it was a design flaw. FN produced it exactly as their engineers specified.
As opposed to SIG which has "Forest Gump Box of Chocolates" levels of random QC, FN is very good about making exactly what is specified, whether that is a diamond or a lump of dog shit.
With the 509, FN brought in a new engineering team and finally got serious about a service handgun. Whether that will continue now that they didn't get the MHS or any big federal LE contracts remains to be seen but the agency testing I've seen indicates it is a real step up from FN's prior service pistols.
Re FN AR barrels, FN makes AR barrels to exactly the spec the customer is willing to pay for. So a $200 FN barrel from company A and not the same things as a $400 barrel from Company B. see above analogy about making exactly what is specified.