Quick Compose - (I don't know if other phones can do compose message in lock screen by using Quick Compose of Textra, but for me, Samsung User, it's not.) In Lock Screen, you don't have to Unlock your phone first to compose quickly in Notification Panel, but rather, even in Lock Screen you can easily compose message by tapping the Quick Compose in Notification panel.

Quick Reply - Same goes with this, when somebody texted you, it notified above the screen and tap, and you can easily Reply even in Lock Screen.