We had a really great experience in Carl's apartment. It is located around the corner from Campo de Fiori and is within easy walking distance of a number of sites including the Pantheon and Piazza Navona.
The apartment itself is very comfortable and has all of the amenities you could need (fully fitted kitchen, washing machine, air conditioning in both rooms, internet, etc.); it is exactly as it is described. The area has many restaurants and bars nearby so it can be very noisy outside but the windows in the apartment do an incredible job of keeping the place quiet.
Aside from the apartment, I really have to thank Carl for being such a wonderful host! We let him know that we'd arrive in Rome a bit early and he made an extra effort to ensure the apartment was cleaned and ready before we arrived. He gave us some really wonderful suggestions on places to eat (and where to get the best gelato around!) and was always quick to respond when we messaged him. He even personally hailed a taxi for us the morning we left to make our travel day a little less stressful.
We had a wonderful time and I'd highly recommend a stay here to anyone looking for somewhere nice to stay in Rome.