My 2.5L had no internal build up at all with 35-40k miles using Mobil 1. No speculation as I actually tore the engine apart.
Also if your engine did have significant build from neglect and improper maintenance then would not removing that build up make the engine more prone to leaks and possible oil starvation. (that debris and build up has to flow through the system before it reaches the oil filter
)
I guess (if I were interested) I'd have to read more up on the product but anything that claims to "clean out" your engine has it's drawbacks when used on an engine that "needs" cleaning.
However most "well maintained" engines do not require internal cleaning anyway.
Also any power or efficiency claims also need to be looked at with a logical mind.
