though i have not used it...my cousin who is chief mechanic of a casa...advised me not to use...additive questions were raised during their seminars......advise ng mga higher ups/engineers---huag na lang...additives in oil are enough to protect your engines...
i used motor up engine oil additive. it decreased the mileage from 16 km/l highway down to 11 km/l. i had to flush the engine twice before the mileage went up again to 15 km/l.
Just like what Happy_Gilomre said, may additives na iyang mga iyan. That is the reason why I stuck with just one brand of oil from the start as different oil companies put differnet additives. Same with gas, I only used one gas [Shell] ever since for the same reason.
And braggingly I say that my engine already has 161k miles in it and still running great...