What's the guarantee that we are not downloading malicious apps that will steal information from our devices.??
I don't have influence of what apps get promoted inside the offerwall. Most of them are safe, I have used similar offerwalls in money earning apps earlier. To prevent your information from being stolen follow these steps:
Do NEVER give root permission to any apps you download from the offerwall
Look at the comments in the play store! If it is a virus someone probably already reported it as such!
Look at the permissions the app needs. NEVER download an app that uses your phone or sends SMS!!!