My wife and I had a combo interview back in 2018. We did not know we would at the time, but suspected it since the I751 and the N400 were both pending (my wife only received a notice for the N400 interview). Regardless, I went with her and the IO pulled me back for a very brief I751 interview essentially reviewing the form and asking if we wanted to add any additional evidence (we brought a copy of our recently filed joint tax return). Then I was escorted back out to the waiting area, and my wife and IO proceeded with the N400 interview. My wife did not get a decision made on the spot for either form, but the experience was positive and shortly, about a week later, we got the I751 approval NOA, and the oath scheduled NOA. I am not sure if the IO did the I751 interview as a formality since we also had an AOS interview three years earlier, but we prepared just the same.
Anyway, plan for it, review your I751 package, and it might be a good idea to gather any additional supporting information you may want to add to it.
Good Luck!