He's basically what we'd like Jeff Green to be. He's younger, a much better 3pt shooter (39% to 30%), and can defend the wing really well. He also scores a high percentage of his points off cuts, which would mesh well with Rondo.
A Rondo, Bradley, Batum back court is very athletic and even more imposing defensively. The biggest problem is prying him away from Portland (who I imagine would be inclined to match a lot of offers). I believe Batum has all star upside, but I wouldn't feel comfortable committing 8 digit money to him based on that still unrealized potential. Conversely, he looks like every bit the prospect that a guy like Paul George is, except a year or so older. His combination of size, athleticism, and outside shooting is pretty rare.