When I first decided to build ReturnMore my original plan was to offer Facebook, FourSquare or Google+ accounts. I’m a user of all these platforms but feel that Facebook has so many users it would be good to just offer Facebook for now. I’m not saying ReturnMore will never work with other sites but right now ReturnMore is exclusively Facebook.
Maybe in the future you will be able to use Twitter, FourSquare or Google+.
Facebook is a great platform to easily connect to as a user, if over 850 million people have a Facebook, it makes sense to use them. There are a lot of limitations with the other sites. I hope you enjoy using ReturnMore with your Facebook account.