When our fab shop had a true blacksmith he used it all the time with great sucess. I know he sometimes applied several applications for certain items.
We did have it in the lab at one time and did section some samples, drive pins, in the lab, but I don't have any of the data as to the thickness of the case imparted. We had a large bucket of the material in the lab that was used mainly on single components.
I have a lock-blade knife that the pin and latch are case harened with Kasnit that is about 40 years old.