It is nice to hear from people who have run a coating for a few years and for a few thousand miles.
The people I know who have had long-term luck with an exhaust manifold coatings have had the manifold(s) coated with a baked ceramic coating (
like Jet Hot $$$ ).
I am now testing a low-tech coating called
Calyx Manifold Dressing, and it is holding up fine - BUT, it has only been on for a little more than one year.