My wife and I spent a short three days in Franck's place, and we really enjoyed it. Franck was there waiting for us after I messaged him from the airport that we were on our way. After a quick tour we got the keys. The apartment is exactly as shown in the pictures. It was in the perfect location for our trip; an easy train ride in from CDG, and also a short two minute walk to the Hotel de Ville Metro which got us anywhere we needed. A 10 minute walk would put you in front of the Notre Dame.
While the apartment is listed as a second story walk up, there's probably three good flights of stairs, including a tight spiral staircase for half of that. Just keep that in mind if lugging heavy bags upstairs.
The windows face other apartments across the building, but on a sunny day there is a lot of light that comes in. The entire apartment was very clean, the bathroom is modern, bed is comfortable, and Internet was reliable. We felt like locals staying here and would stay here again.