From what i read online,those additives/cleaners work for the area after the valves;inside the cyclinder chamber only.
To clean the area above,some use water to inject into the manifold,walnut blasting,removing the intake manifold and scrubbing it like a bbq pit (with brake cleaner etc) and lastly to install a methonol injection kit (i can't confirm this as i was not able to find out where the methonol/water is injected to,above the valves like in a conventional port injection engine or directly in into the cylinder,if its above,then theres cleaning,if its below then i guess not).
For me,the methonol was out as i did not want a water bottle in the boot,also heard 1 horror story that the spraying of the water method cause a chunk of carbon build up to get thrown into the cylinder and caused the pistons to jam. So i was left with either using brake cleaner method or using walnut shells...
Honestly,the effect of cleaning the valves was not that great,to me..insiginificant but for that amount i paid...peace of mind was well worth it.