I did read the article and I don't find what the author thinks is a "nice illustration of a cartesian product" easy to grok at all. Similarly, I think I would have found the the diagrams further down hard to understand versus a Venn diagram.

But that wasn't my point; if other people find these illustrations helpful, that's awesome and I wouldn't want to stop someone inventing something new and useful. My point was that I violently disagree with one-size-fits-all proclamations like "Say NO to Venn Diagrams."

The hardest part of joins is remembering which is which. Venn diagrams are used specifically because they solve that problem with the inner/outer/left/right terminology.

His visualizations ultimately help nothing. You have to stare at them for a while to see what the pattern is, but there's absolutely no mnemonic hook to remember what's what, so in the end all you learn from his visualizations are that there exist different ways to slice and dice the products of sets, which is already a given if you're trying to figure out what the differences are.