the reliablity is dependant on which Russian factory cranked them out according to the Saiga forums
I've never heard this. Did not know Izhmash had multiple places that manufactured Saigas... Do you have any info on this?
While there are definitely some small differences in the multiple Saiga-12's I've handled they have all been very reliable.
The only issues I've seen are due to cheap US made mags. AGP, Surefire, Promags.
As with any gas operated auto there are certain very light loads you can't use with certain guns.
Wally World bulk Winchester birdshot is known to by light.