This application called as 'Appnana' is giving free gift cards, are they having income?

This application literally gives you money through offers and stuffs @@ Are they actually gaining any income? And that sharing codes stuff, is there a maximal of how many people's codes may be entered in a day? And also, I am using it, I am saving it. The problem is, it is only valid in US stores, what if I am not in US? Please help :( -TL