Last write wins is not handling data sync, it's washing your hands of it.

Your users will be frustrated.

Firebase is offline-resistant more so than offline-first I’d argue.

The (JS) frontend SDK can be set to either online or offline mode. When in online mode, it seems to insist on downloading full copies of records, even when a version is somewhere in the local cache, slowing things down and incurring cost. Some optimisation could have been applied here, I didn't find anything about it in the docs. Does this match others experience?

Firebase works until you want a different conflict resolution then last-write-wins. It is also only offline first if the user is authenticated. Otherwise you need a connection to the servers before using the local state.

I mentioned Realm because thats what Im familiar with but yeah Firebase is also a good choice if you want a client-server setup.

Ah yes. Convenience is how Big Tech gets all data to pass through it.