i've done the piston coating thing a couple of times. i was in the "usual" situation trying to tighten clearances up. i've found that it's not a long term or permanent cure. it doesn't hurt anything and maybe some advantages in a special situation. i may try it again someday and i'm not trying to discourage it's use but it's soft stuff made to wear and is no cure for missing cast iron. i have no preference for who does the coating but you might ask about if there's something with a long term durability factor.