I am using up my coats and clark and replacing in with Aurofil and Superior threads. It became apparent very quickly with my new Bernina just how much C&C sheds in the machine. Better to pay a little more for a better quality thread than to screw up my tension disks.
I think C&C works fine in older, mechanical machines. No significant shedding in those that I could see. There was a period of time when C&C had really crappy thread (slubs here and there), but that problem appears to have been eliminated.