The app is currently not available on Play store. You can opt to become a beta tester.
If you want to be a beta tester, log on to https://play.google.com/apps/testing/co.zenbrowser
Once you agree to be a beta tester, you will be taken to the download page via Google Play Store.
The browser promises that it credits back the data used on the browser. Since the app is currently not public, it can only be checked by the beta testers.