Just had my interview this morning. The interview appointment was originally for N400 but it became a combo for both i751 and N400. It lasted an hour and 5 minutes, with a short power interruption in between (!!!).
Upon the officer learning I had a pending i751, she informed me she needed to ask me a few questions about my ROC application. She wrote down my answers on a piece of paper then called my husband in, telling him she would ask him questions about our marriage and requested me to not say anything or nod or shake my head. She asked if my husband had any documents on him that would prove we are living together and are operating as a married couple. My husband was surprised because he didn't prepare anything. (Side note: I knew he had his driver's license and health insurance card on him and I had the rest of the other stuff anyway so I didn't ask him to prepare anything else.) He presented his driver's license and health insurance card. The officer asked my husband the same questions she asked me and everything was consistent. After the Q&A, she asked my husband to wait in the waiting area. She made copies of the documents and told me she approved my and my kids' i751.
She explained that she needed to adjudicate the i751. Otherwise, we can't proceed with the citizenship interview (which I already knew but didn't tell her; also the very reason my husband came).
For the N400 part, she did the civics test first, then reading and writing. She asked me the yes/no questions on the form, my height, phone number, address and job. She then asked me if I understand the oath of allegiance fully. She then asked me to sign my application, printed a page which she handed to me, and congratulated me. She said I should receive the oath schedule in the mail.
It was a long interview but there were a lot of light moments where we laughed. I was nervous at first because she looked stern at first. I thought she was going to get frustrated because of the surprise pending i751, power interruption, and documents that kept jamming in her scanner, but she was very graceful throughout. It was a nice experience overall.