I have done a fair bit of research since starting this thread.
Spoke to engine builders and numerous engine cleaners, these are my findings.
As the product tester for the owners club, I'm always testing something. Some months it feels like I do as many miles on a Dyno as on the road.
There seems to be a few ways advertised of removing carbon.
Putting some gas or fluid through the intake.
This is the one I have questions with, they make some bold claims. Regain lost power, better fuel. So what better person to test. I offered a bore scope my car, Dyno run it have it cleaned and repeat the process. I have made this offer to countless operators with not one taking me up on my offer.
Being involved the motor trade all my live and my father before me. I have seen my fair share of carbon removals, I takes grinding or blasting. So while I have no doubt in the various blasting processes, I have serious doubts on the chemical process. Now the chemical process does more then likely remove some contaminants, can not see carbon being one.
Where you have people swearing they felt a diferance after, could be some gunk removed or the placebo effect.
Even someone like myself that tests all day everyday, have to check placebo effect. If you get told this will change abc on your car. You are now paying extra attention to abc. Abc will feel different, I get someone else to double check any findings I'm unsure of.
In summing up
Gasfluid clean .... may clean something but not carbon. Cleaners have said it's more ptoventitive then reactive, they also admit running premium feul will have the same effect.
Blasting with media ... proven results