Comment by rockwotj

> Firebase Realtime can be more efficient, as it can tell if a permission check has passed statically. I am not sure if Firestore works this way.

Firestore's rules are also able to prove before the query runs if the query will only return data that the user has access to according to the rules. That's a pretty important property that "rules aren't filters" because it prevents bad actors from DDOSing your system. My former colleague wrote about this: https://medium.com/firebase-developers/what-does-it-mean-tha...