The theory is that ceramic coating the outer tube will reduce the heat radiating out.
I can testify the thing works on my 4-cylinder 400 Katana - you can touch it right after having had a ride which is quite surprising.
I hope the effect will be enough to reduce the number of "fan on" cycles on the DN, as well as reduce the heat on my right leg on warm days !!! I feared my rain pants would melt in Italy
And the heat generated by the engine - will go where..?
It does not reduce, because amount of fuel mixture burned will remain the same, amount of energy released remain the same. It's high school physics we know it from.
Gasoline engines will leave heat generated by burning fuel mainly in two ways: by liquid cooling (or air cooling) system and by exhaust gases. If you will invent some system making exhaust pipes cooler, like covering them with glassfiber rags for example, the amount of heat leaving the engine in given conditions still remain the same.
While you are driving against the airflow (like normal driving you do) it will cool the engine thru radiator and the cooling agent (the cooling liquid). If standing and not moving the same kind of airflow (the "wind") will be generated by radiator's blower. But some considerable amount of heat will also leave the engine with hot exhaust gases.
The surface covering thin ceramic material may make the surface of exhaust pipes a bit cooler (probably not much), but heat amount leaving engine thru the radiator will remain.
The temperature of the engine fluctuates in quite a big amounts. I installed a digital engine thermometer on DN and as the result I have seen fully warmed engine cooling liquide temperatures between 68C...99C degrees. The fan kicks in when engine temperature is about 94..95C deg. and stops when it is 90...92C deg. And 68C deg. it is while driving steady about 100kmh at +12C deg. or lower weather.