Incredible value! The unit we stayed in is on the 4th floor and does have a balcony overlooking the dome of St. Peters. The flat is perfectly comfortable and quiet and the AC works great. It is on the small side, probably less than 400 sq ft, and the shower pan is probably 22x22 inches. But it is just a few blocks from the Vatican and less to the local train station / bus depot.
Marina was helpful and responsive and arranged everything for our late arrival. She was helpful in recommending restaurants and shopping and explaining the best way to get around on the bus with a day or multi-day pass. I can't stress enough how gracious and helpful Marina was, even helping me with some special arrangements. Google maps got us to the address, but I did use street view first and Marina thoughtfully sent annotated photos of the entrance and other pertinent items. For those driving, there is street parking. I suggest you look at google maps satellite image view to see where your options are. We were lucky and parked fairly close by pulling almost vertically up a hill under the trees. My partner is a big guy and despite the tiny shower, he agrees that we'd come back to Marina's place without hesitation. :)