Some people believe that it worked for them. Without a carefully controlled testing environment, and repeated observations, it’s impossible to know if this or some other confounding factor played a role.
I think the old “if it sounds too good to be true” adage is still intact here…
As per what I have been told, the vehicles in question had catalyst efficiency error codes, which went away with use of the product. I suppose it’s possible the codes went away spontaneously, but I think that’s highly unlikely. Again, how bad the cats were is unknown but I’ll bet they were right at the edge of working properly. YMMV