I work for a company out of Bluffdale, UT. and we manufacture an additive that boasts similar claims to that of zmax, dura lube prolong, and those sort of campanies. We are new and still getting testing results completed, but we have had very positive feedback thus far. What additives are most used and trusted out there by large fleets and why?
Well to answer your question in my opinion more and more people are becoming less trusting in oil additives. Mainly because of all the fraud products out there. Now I am not saying all people think this way but its starting to become more and more. There are three things I think people should look for and you as a company should do.
1. Make sure the product has had testing done and shows positive results. (There is no harmful effects to the engine in the long term)
2. That the product has documentation
3. The product has been SEO approved. Yes I know its expensive to have done but, that is what truckers look for. Because only a small amount of products that go through the testing unless they work pass.
If you go to http://www.oiladditive.tagzap.org they give you tips on using an oil additive what to look for, how you can benefit from it, etc. The product that they recommend has all 3 of these qualifications.
Hope that helps! good luck with everything