Usually, it comes in matte finishes and is supposed to be hard wearing. Popular alternative for coating aluminum pieces instead of anodizing.
The hard wearing part is an absolute lie...
It's really loved for firearms because it's extremely heat resistant, but it's quite prone to scratches...
Ceramic coatings usually come in 5 to 50 microns, Cerakote is usually below 25 microns without compromising quality...
That's so thin that firearms people usually don't even care to mask screw threads since it's so thin it just doesn't matter...
As for the seatpost: I had a talk to another owner of the bike who had the exact same problem with the seatpost even without painting or coating it ... Even worse than with mine - his seatpost seams to be completely stuck now...
I hope I will not have to change sale height too soon because it's very close to stuck on mine as well...
I just believe that this is one of the weaknesses of this particular frameset...
I know why I love my round seatposts...