I've had ceramic coatings done on exhaust parts before, but that was on turbo applications where you're dealing with much higher temps. Was it worth it? No idea, never took pre/post temps to find out, but it looked pretty No real drawbacks that I'm aware of, but obviously you need a total coating to prevent anything getting underneath it and also reasonably thick so it does the job,
On relatively low power NA (i.e. anything short of pure race engines) I wouldn't bother if I'm honest, unless it's for the looks.