I spent 4 days at François's flat and I sum it up as a perfect choice. First and foremost, the location is fantastic. It is in a very short walking distance from places like the Pompidou Museum and Ile de la Cité, and is next to a square with many small pubs and other places where you can get a late drink/snack. The apartment is also a minute of walk away from the central Metro/RER station of Chatelet, which means it is very convenient both as a starting point for exploring the city and with with regard to getting from/to the airport.
The communication with François was very smooth. He explained everything in advance and responded very quickly to questions I had before and during my stay. The self-check-in was very easy to do. The flat is clean, well-heated and designed beautifully, and the living room is large and comfortable. I highly recommend it!