Courier vs Firebase Cloud Messaging

Courier has no write-up on Specifiction yet; its figures are above.

Firebase Cloud Messaging (FCM) delivers messages and notifications between servers and client devices over a reliable, battery-efficient connection. Senders can choose notification messages for display to users or data messages for an app to process. Messages can go to an individual device, groups of devices, or devices subscribed to topics; instant-messaging payloads can be up to 4096 bytes. Sending options include the Firebase Admin SDK, the FCM server protocol, and the Firebase console Notifications composer. Notification messages integrate with Google Analytics for engagement and conversion tracking, and A/B Testing with Remote Config supports testing notification variants. Setup guides cover Apple platforms, Android, web, Flutter, Unity, and C++. The JavaScript API works in browsers that support the Push API, including Chrome extensions using it. The web SDK requires HTTPS. FCM is free: its listed plan is free. Data in transit is protected with TLS, but FCM has no built-in end-to-end encryption; apps handling sensitive data must provide that protection themselves.