Opera Max uses a Virtual Private Network (VPN) to measure the amount of data going through your phone. All data requests eventually are sent through Opera's servers and are compressed to optimize video, images, and websites. The app only keeps track of the amount of data that you use and the amount that you save. Opera Max will not work on encrypted apps, like some of the ones on Facebook, but every other app is fair game to be compressed.
Opera is seeking beta testers for the app. It seeks those in the U.S. with an Android device running Android 4.0 and higher. To join the beta testing, go to Opera's Google+ community, opt in for the beta test, and download the app. Yes, you must agree to the End User's license agreement. Once that is done, Opera says you'll have more control over how much data you use. Opera says it wants as a beta tester, the kind of person who wants to know which apps are using the most data.
While Opera Max is only available for Android users in the U.S., the company says it plans on expanding the number of countries and platforms that the app will be available for.
source: Opera via Engadget