Anybody have any experience or thoughts on it? I am always very warry of any of these additives and their claims, but I must admit when I put duralube in my wife's DeVille, I noticed an incredible increase in the smootness of start up. From all the informercials I have seen on Speedvision Zmax seems the most credible. So, my questions are, does it do what it claims, and is it necessary? I would also be interested in hearing about their tranny fluid additive.