I have no idea how well the Jet-Hot coating will reduce the heat radiated from the headers, but in theory at least, a shiny surface has much less emissivity than a black body.

Jet-Hot has been around for many years and I've never heard anything but good about the product. My Spyder headers are Jet-Hot coated and they have stayed shiny for the last 5 years. I did not measure engine compartment temps before and after the installation.