I really like this recipe @hickst, the content is great!

One bit of concrete feedback I would provide, however, is that the solution is rather discussion-heavy.  I'd prefer to see most of the explanation here (and possibly some of the examples) shift into the discussion. It may be appropriate to include one or two succinct examples demonstrating a normal merge, a destructive merge (overwriting left to right), and a merge-with to retain information. Then, in the discussion explain precisely how these functions work and behave.

Keep up the good work!