Me and my husband stayed for 9 nights and had just great experience from the beginning to the end. The flat was spotless, in a perfect condition and all the techniques were working fine (except the laundry dryer). Bed was very comfortable and despite the winter time, it was pretty warm at home. Fabrizio himself was exceptionally generous and very caring, and his recommendations were perfect. The area of the flat is not overtouristic (fortunately!), but still has good amount of worth visiting restaurants and enotecas. Though in the street could be a bit noisy during the weekend nights due to some nearby clubs, but since we are not a light sleepers, it didn't bother us at all. There is also nearby Testaccio farmers market with delicious and not expensive fresh takeaway Italian food. Another place in the area is Remo Pizzeria where we had one of the best pizzas we have ever tasted.
The only thing I would notice (since it's one of the criteria for me -to have warm floor) is that the floor in the pictures looks like wooden, but it's wood-looking stone floor )
All in all, we would definitely stay again at The Ancient Walls :)