I worked full time on a pretty seriously-trafficed product based on MongoDB for 3 years and I still don't know of anywhere I'd want to use MongoDB. I'd basically always want either a DB with a schema or a super fast opaque-store style cache.
Also, their hosted offerings (MongoDB Atlas) were not well operated and they took down our company for 2 days. Our MongoDB instance stopped accepting new connections and restarting our instance via their control panel didn't bring it back up and then their support literally said "we don't know why this happened or how to fix it" for like a day and a half, while we were on their highest tier ultra platinum support contract. Ultimately, we had to do 24 hours of research and then tell their own support how to fix the problem using their special shell access. If I recall correctly, it was some issue with WiredTiger (an internal component of the Mongo version we were using).
After that experience, I'd never use anything produced by MongoDB for anything; we moved everything that we possibly could out of Mongo and into more traditional RDBMS (PostgreSQL) and never had to deal with issues like that again.
This is a pretty common experience with mongo tools and support, sadly.
Recently I ran into a tool that spat out "you probably want to use this option!". We paid for enterprise support so I asked why this option was not documented, and they said because it is dangerous. Can you imagine if the "-f" for rm wasn't in the man pages? Ridiculous
Also, their hosted offerings (MongoDB Atlas) were not well operated and they took down our company for 2 days. Our MongoDB instance stopped accepting new connections and restarting our instance via their control panel didn't bring it back up and then their support literally said "we don't know why this happened or how to fix it" for like a day and a half, while we were on their highest tier ultra platinum support contract. Ultimately, we had to do 24 hours of research and then tell their own support how to fix the problem using their special shell access. If I recall correctly, it was some issue with WiredTiger (an internal component of the Mongo version we were using).
After that experience, I'd never use anything produced by MongoDB for anything; we moved everything that we possibly could out of Mongo and into more traditional RDBMS (PostgreSQL) and never had to deal with issues like that again.