I had the combo interview today and it was a touch more mixed than I would have liked.
The N400 part was open and shut. Nailed the questions and English tests due to studying and from speaking English since I was 4.
The I751 portion didn't go as well as I would have liked. We brought a bunch of documents and photos, but the officer didn't seem to care about most of this. He asked me why our driver licenses had different addresses (one was old and nearing expiration) and seemed to take issue with that. He also didn't like that we didn't have bank statements from our savings account where we pay our mortgage from (we instead took statements from only our checking account). He also didn't seem to care about the actual legally recorded mortgage document, which seemed odd.
He asked us some general questions but never cross-examined us. As in, he asked us about ourselves, never each other. This section was also very short. Maybe 10 minutes?
At the end of the interview he confirmed that he was satisfied with the N400 interview but needed to do some "checking on background things" to process the I751. We confirmed he didn't want to see any photos or any other documents and then left. Of note, he did not give us any paperwork detailing the outcome of the N400 interview.