The flat is very clean and spacious, lot's of sunlight streaming in and the kitchen is well equipped and nicely furnished. The AC in the living room was godsend but I wished for a fan in the bedroom because Rome doesn't cool down much at night in summer.
Although I haven't met Carlos communication was easy and he promptly helped us when we made a mistake (locked ourselves out..).
The only thing I hadn't realized at the time of booking was that Carlos has a flat on the upper floor where he has to walk through the renters apartment to get to it. He was never there during our two week stay though.
We also chose the flat for the location in San Lorenzo (close to Termini and Sapienza) but if your main goal are the tourist attractions then the location is not ideal since San Lorenzo is badly connected to public transport.
San Lorenzo however is a really cool and charming area where you'll hardly ever meet another tourist with lot's of bars, restaurants and shops.