I am not sure of the website credentials as they do not show who finances them or who the "expert is" but I suspect they are being green and do not want anyone adding burnt oil to the exhuast gases. We all know the definition of an expert. X being the unknown quantity and a spurt is a drip under pressure!LOL
The bit about carbon deposit build up might be true if you add too much and use it constantly.
I just do it every fourth tank full or thereabouts.
To me the practical evidence is clear.
I have always found the engine quieter when I use the treatment - this works virtually immediately.
I have 39 years of practical experience having done well in excess of 500,000 miles in a variety of vehicles. The only time I ever experienced carbon deposits was way back in 1968 when I was a student in Bradford and ran my Cooper S on Nafta fuel - that carboned up my cylinder head in 6 months ! Stopped using Nafta - problem sorted!
On what what basis is the unknown fuel expert working from what is his evidence to support his claims?