If your friend is buying those chips thinking they do what they clame to do, then I have bridge in San Francisco to sell him...
I am kind of curious to crack one of those O2 sensor ones open to see what's inside that "manipulates the signal every microsecond". I seriously doubt it's an active component. To me, it looks like it's probably a small metal canister filled with pure snake oil and that's why it's so expensive.
Oh, and an interesting thing to note on the O2 sensor one... one section of the page says it has a lifetime warranty; further down it says it has a 10 year warranty.
As far as the potentiometer one goes, I wouldn't trust that one either.