This apartment is fantastic. Right at the heart of the city, a stone's throw away from Piazza Navona, a 10-15 minute walk to the Pantheon and Trevi, and around 25 minutes to the Colosseum. We walked pretty much everywhere, it was great to stumble upon beautiful churches and landmarks on the way.
The apartment is also next to a tasty gelato place, Roscioli cafe where we had coffee almost every morning, and right next to the market square. Don't worry about the noise - the windows are thick and great at insulating sound, I didn't get woken up once and slept right next to the main street.
Tatiana was fantastic - answered all my questions in a timely manner, had a very straightforward check-in process, and gave me a few tips on food spots to boot.
One big recommendation from me is the (free) Rick Steves Heart of Rome walking tour, download the Rick Steves Audio Europe and the walking tour plus a bunch of other tours for landmarks in Rome are on there. One added benefit is that the walking tour starts at Campo dei Fiori which is just down the road from the apartment!