2 questions on raix:push (or other push) and gcm / fcm

I’ve been working on making GCM push notifications work for way longer than I want to admit.

Question 1: On my hybrid app, I have now a button “send test notification”. This works if I go to my staging server and click it. If I go to the same page on my Android app itself, I do not receive the notification, even though GCM diagnostics will say it was delivered. Is this even expected behavior? Maybe an app is not exactly supposed to be able to send itself a notification? Yet from the Google Play Store, the Push Notification Tester appears to do that (maybe there is more going on behind the scenes).

Question 2: While trying to learn something from GCM diagnostics, I went to check GCM diagnostics and today Google is recommending to use Firebase FCM instead. There is a link for migrating from GCM to FCM. Everything in that link is Greek to me, as it appears to only care about native Android development (as best I can tell). Does anybody know anything more about whether I need to be thinking in terms of FCM for my meteor app that is only now/soon having push notifications?