I had to code-review a Django app using Firebase as a DB and swore never again. He did features and promised to do validation and security later by going to their editor and writing Javascript files. Django lets him write valid forms and correct SQL queries in almost same lines of code. Pagination was a pain in current version and present only in a version forever in beta. All the hard work coaching him on exceptions went out of the window.

An Android dev finally enlightened me where Firebase shines: offline sync of mobile to a server by eliminating lots of explicit CRUD calls and error handling.