The Callback is completely de-Googled, but thanks to the compatibility layer, Sailfish OS can run over 99% of Android apps. That means you still have access to essentials like WhatsApp, Google Maps, Spotify, Signal, and iMessage via a third-party solution that needs temporary access to a Mac.

In other words no Android app compatibility unless you already own a Mac. Seems like a strange way to have Android .apk compatibility but I don't know the specifics of how Sailfish OS works, maybe it has other macOS dependencies.

That aside it could be interesting for people not needing anything Android related at all.