Their sandboxed implementation allows access to the entire profile. They even suggest creating a profile for those apps that require the Google play services. Microg at least removes Google as much as functionally possible in order to limit the data google receives. You lose some functionality, but not enough to cause any issues for me, even not with banking apps.

As far as the persistent notification for Signal: I can disable it, but won’t receive notifications of new messages until I open the app; or I can hide it, but then won’t receive any popup notifications at all (technically, they do come up, but they’re hidden). Haven’t found a way to hide the persistent notification and still receive popup notifications of new messages.

I think what GrapheneOS is doing with Google play services is amazing and, depending on your needs, may be better than microg. It’s just not there yet for me. Additionally, google can suddenly decide that using Google play services like this is against their ToS and submit a cease and desist order against them, and GrapheneOS’s implementation becomes illegal to distribute.