Google’s John Mueller said on Twitter that Google does not currently use isRelatedTo or isSimilarTo schema for product schema in web search. He said as far as he knows, they do not use it. isRelatedTo schema is a pointer to another, somehow related product (or multiple products). isSimilarTo is a pointer to another, functionally similar product (or multiple products). John said “I’m pretty sure we don’t use them in web search — I don’t know how you’d use them outside of search.” Forum discussion at Twitter.