A different perspective, recently used some Chinese made mandrel mounted disks bought at a car show. It seemed I was having to work the same area much longer than expected. I changed over to an older disk, bought years ago from, most likely a hardware store. Hey, I"m old and can't remember the source, cut an old coot some slack. Anywho, the old disk made short work of the effort. My best guess is the steel quality is different; one softer than the other.
