Admin SDK vs. making REST calls (both server-side)

[Derrick Chao]

Hello,

I have a bit of a unique use case that I think is different than the usual client-side SDK vs. Admin SDK questions. I currently have two apps with Realtime Databases that communicate with one another, and use a Cloud Function and Firebase Admin SDK (Node.js) to communicate from one app to the other's database. This has been working well.

We would like to reduce the level of privileged access between the two apps and create more separation between the entities, so I am now considering migrating from using the Admin SDK to instead making standard HTTP rest calls on the server (using the Firebase REST API), treating communication between the two apps more like communication between third party APIs. 

If making REST calls from a Cloud Function instead of using the Admin SDK, will there be any meaningful changes to performance or costs? Is the Admin SDK just using REST under the hood?

Thanks,

Derrick