That looks great for the developer but for the user it's a different story. To benefit from the free install/use, you have to install first Amazon Underground on your device and this application needs almost all existing permissions. When you know that selling data about customers is one of the most profitable source of income of this industry, you understand that the product, it's you ! As an user, I don't want it on my devices. I don't want to share my emails, SMS, contacts, agenda, etc. with Amazon. Most users won't be aware of that or won't understand the risk. They will see only the advantage to get free apps/games. That's why, as a developper, I have to wonder whether it's ethical to offer such a choice to users.