I will start with the positives. We heard from the person meeting us at the apartment several days before check in, explaining what we need to do to get the key. She was there, waiting on us the day we arrived. She also was kind to explain the how to get to the grocery store/major attractions.
The apartment did not work very well for us (a family of 6, including two children ages 5 and 8). First, there a restaurant across the street and a bar around the corner. The first night we were there both the restaurant patrons and the bar goers stayed way past 1 am talking and signing loudly. The apartment has older windows and we could not sleep. Then the trash pick up happened every morning we were there around 5:30 am, waking us up.
Also, there are two window AC units, which kept shutting down periodically, unable to keep up. There are several fans throughout the place, but they were of little help.
The kitchen was not very well stocked -we had to buy such basics as salt.
The floors were very dirty.
The two beds in one of the bedrooms were very narrow.
There was a very colorful homeless person who we saw every day on the way to Piazza Navona - be careful, she was doing some very inappropriate things.
Overall, if you are looking for a historic, centrally located apartment with a good value, and plan to stay up late, you will love the apartment. It just wasn't for us.