Bob, at least the FAL has a gas adjust. If you'd switched lots like that with a CETME you might have written "it only functioned reliably with certain lots of ammunition"...
I think they are a good buy for the money. You'll spend another hundred dollars or so really making the gun right, but you are still well underneath the next step in FALs, which is the M444 metric (which needs some of the same parts replaced to run right!)
You'll want a new fire control group, maybe some new springs, a US made gas piston, and probably a different profile stock. After that it'll run just as well as guns costing $500 more.