I have a Century-made FAL which is an IMBEL kit on a Century receiver. Bought it off a THR member here. It had some issues with cycling.
Total cost to fix it up right was less than $20, and an hour or so of my time.
The gas piston was undersized and had been packed with black grease. Picked up a used like new gas piston from the internet. Cleaned out the grease.
The recoil spring was twisted/bent, and the tube was packed with black grease. Replaced the recoil spring and cleaned out the black grease.
I had to lap the receiver rails where the mag went in.
I had to remove a little material where the gas piston comes through the upper above the chamber.
Presto, suddenly a gun that was a jamomatic was now 100%.
I owned an L1A1 kit Century with the Bell & Carlson butthole stock, and it was 100%. Inch gun that took metric mags- best of all worlds!
I also have built several FALs myself from parts kits on Century receivers. Now that I know what I am doing, all of them ran 100% right off of my bench.
As far as CETMEs go, I haven't owned one, but I've seen some with ground bolts and other issues. Century just slaps 'em together and makes 'em work as best they can, with no test firing.