Bender has graced the Barth community with his magnus opus, a product of his extensive studies at Princeton Theological. The usefulness of this text comes through on several counts.
1) Its breadth. Bender's work eclipses the gains of former studies on Barth's ecclesiology, covering his pre-Romans work through his mature stance. As Barth was anything but static on this issue, an overview is necessary. This book can be compared to Bruce McCormack's in scope.
2) Its use of the Gottingen Dogmatics. Bender finds some of the richest material in not-yet-translated German texts. As Barth's evolution is so closely tied to his Christology, scholars have been hurt by the lack of his 1924-5 lectures in english (a second volume is to be released soon, yes?). The mature writings of the Swiss theologian come into better focus by filling in these holes.
3) Its fruitfulness. Bender is right to contend that Barth's later work bears the mark of Chalcedonian logic, ecclesiology or any other locus. I've found the expensive book worth its price - even with my own studies pursuing Barth's doctrine of the resurrection.
4) Its simplicity. We should all be envious of Bender's ability to write crisply. While the footnotes can be dizzying, the central text shows confidence with its clarity in speech and content. If Karl himself only possessed this virtue!
All this to say, it serves one well to have this book within arm's length of the Church Dogmatics.