Emily, the belly bandit isn't going to give you the support that belly binding is intended to do. Many cultures bind post birth. All I can say from my experience that it wasn't too bad after my first, but with my second, I felt like my insides were falling out and it was a disturbing feeling. I grabbed a baby wrap, laid on it and rolled myself up. It was a little constricting to sit, but mostly just because I was using so much fabric. It felt so, so, so good. I agree that there are some more extreme ways to go about it though.
I believe that the most common reason for binding is to suppport the stomach muscles as everything moves back into it's prepregnancy place. The abdominals are so stretched that it can be really hard on your back as this adjustment happens. I felt like binding made this process happen more quickly and more comfortably. I do think you can bind tightly to push the pelvis back in and those more extreme things, but for me, it's for comfort. It's a huge bonus that it helped me get into prepregnancy clothes more quickly though!