It's a prototype to test the materials, engine, process etc. Since it's only ever going to do little hops like this one, it doesn't need to be aerodynamic.
They are testing on a path to be able to land from orbit. Starting with short hops by prototypes that get iteratively improved is the same methodology that allowed them to be able to land their currently operating Falcon 9.
They are the only one to ever achieve this. It's a big deal because everyone else builds a $100M rocket and then throws it away because it can't land. Reusable rockets have the potential to make açcess to space much cheaper.
Yep, basically. The biggest difference is that this is the second stage. With this new rocket, both the first stage and second stage will be fully reusable. The Falcon 9 second stage is thrown away each launch.
