This all just my opinion, and it may just be that my knowledge of what's missing biases me towards the fuller account. You might want to look at a review by someone who hasn't read the original to see what they thought of it, it may not seem as choppy to them. Ultimately, you get a pretty good overview of the events of his life, and I still have the same caution towards his view of Catholicism, like I mentioned in my review of the unabridged account of his life, it seems that he may have thought that the beliefs of Catholicism were accurate enough that the people who hold to them are saved. It makes me a bit nervous of what he actually believed about the salvation of God. If he actually loved Roman Catholics, then he would try to explain to them what God's word actually says about there being only one Mediator between us and God, and how our works will not save us, earn us any points before God, nor will the 'merits' of the saints give us any 'clout' before God. God Himself provided us Righteousness in His Son Jesus Christ.
All in all, I just felt that one didn't get 'acquainted' with Bonhoeffer in this abridgement, it was more like a recounting of events in his life rather than a look at what was going on in the man himself. But again, some people may like summaries.
I received a free review copy of this book from the Booklook blogger program in exchange for my review which did not have to be favorable.