Unlike Hangouts, the new Messenger handles traditional text messages (SMS) only. So this doesn't include chats sent through the Google instant messaging tool, just everyday texts.
Although it only works with SMS, Messenger includes some new and interesting features. For example, you can block any number from the app itself so you no longer receive texts from them. Similarly, you can set up times when you don't want to receive any text messages at all.
The most notable change is that, unlike the previous text management app, Messenger's interface is much cleaner and more elegant. And you can even use it to send photos and videos directly to your contacts.
Messenger is a great tool for managing messages and comes with the Google seal of quality, which is reassuring when it comes to managing content as sensitive as text messages.
Requires Android 4.1 or higher