I am associate with a fellow here in Houston who owns a company which coats engine parts for NASCAR engines as well as other race venue engines. He also is a great place to have ceramic coating to exhaust manifolds on show and classic vehicles. He is very well schooled in engine lubrication. I asked him once about M1 and got a hell of a diatribe of lubrication education, and do not use M1 partially from his perspective, but from the YJ I mentioned and other engines I've worked on that did not impress me as to the condition of internal components wear marks that had been on M1.
GM makes am oil additive which I use in Non VVT engines. Because it contains Zinc Phosphate, it can no longer be legally sold as an oil additive, so now it is sold as "assembly lube". It is slightly less thick as molasses, so it might cause flow problems with VVT systems.
As far as the "damage" to catalytic converters go, my philosophy is that if the converter fails at 200,000 miles as a result of the stuff being used, I can replace the converter for a thousand dollars or less in the majority of cases. Gee, now, let's see! A new engine, all in, is way north of 5 grand in most instances these days....For the long term owner such as myself and my customers, it's a no brainer.