I think those aditives aren't bad ot use in a old car with worn out rings and seals that could use a little bit of teflon to plug all teh leaks and smooth things out. But any car made after around '95. I wouldn't use it.

Never ever ever use it in a motorcycle with a wet clutch. It will ruin your clutch plates since the teflon will coat the friction surfaces.

It would not suprise me if that stuff clogs certain oil filters with hgiher effeciency filtration.