MongoDB is a fun toy database right now, nothing more. Unless you have the resources to fix every problem that comes up, you should use a mature database like Postgres or MySQL (MySQL is not as terrible as some might think).
And I would disagree that Mongo is a "toy". We use it as part of our core EDW and we have petabytes of data in our data lake. No issues what so ever.
One that you don't even realize until you compare the data with canonical source.