From Wikipedia:
The company along with several others including Valvoline Engine Treatment, Slick 50 Engine Treatment, STP Engine Treatment, and Motor Up Corporation, was investigated by the Federal Trade Commission in 1999-2000 and was found to have no competent or reliable evidence substantiating these claims about its performance.[3] In March 2000, Dura Lube and competitor Motor Up both settled Federal Trade Commission charges that performance claims for their engine treatments were deceptive and unsubstantiated. The two settlements barred false and unsubstantiated claims about the performance, benefits, efficacy, or attributes of these products. In addition, As one of several industry companies penalized by the FTC, Dura Lube paid $2 million in consumer redress to be distributed by the FTC. The FTC had previously halted allegedly deceptive ads for Prolong Engine Treatment, Valvoline Engine Treatment, Slick 50 Engine Treatment and STP Engine Treatment.
Any products offered by these companies are simply an attempt to take money from your wallet and put it in theirs.