The most common use case for Mongo is storing relational data for web apps, and the most common outcome for those apps is complete dysfunction. How do I know that’s the most common use case? Aside from my own anecdotal experience, you just need look at the features those DBs implement. They’re constantly implementing new RDBMS-like and ACID-like features. They wouldn’t be doing that if that wasn’t their market. Why does this happen? Because people who don’t know better keep thinking that they can somehow work around the constraints, and just make a mongo (or dynamo) RDBMS work somehow. It is an apples to oranges comparison. But it’s worth making, because of the large number of people who think it’s ok to substitute oranges into apple pie recipes.