We had a very nice time at Costanza's ; the flat is indeed very spacious (2 bedrooms + 2 bathrooms, ideal for two couples), clean and well furnished.
Our host was extremely helpful : we encountered some plumbing difficulties that she was able to fix within a matter of hours, thanks to her unfailing receptiveness.
The neighbourhood, if not particularly interesting in itself, is super quiet and feels very safe, the metro is literally 3 minutes away, the nearest supermarket only a handful more. And the gelateria on the street's corner was a delicious surprise :)
All in all, an excellent adress !