We had to start with Facebook because getting people to use their real identity deters bad behavior. We'll add Twitter login in a few weeks. We're setting up community management and moderation now.
It's fundamentally different than Instagram: the focus on on the words, picture is secondary. Instagram is all about a beautiful photo, and then maybe you'll read the comments. Because you don't need a good picture in the first place, Tiny Review lends itself to different situations.
I'm really loving this app right now. For me, it has largely replaced Instagram. With Instagram I feel like I am filtering the world around me. Whereas with Tiny Review it feels much more creative. I am adding, not filtering. I get to add so much more of my personality and emotion into Tiny Reviews than I am into Instagrams. That said this app will only get better when the founders tailor the app in some specific ways: namely, remove location requirement and add full twitter support. I hear they are working as fast as they can on both.