Jean’s flat is nice. It’s well located around a lot of bars and restaurants (although a slightly nicer neighbourhood is Le Marais, although also more expensive!) The flat is well equipped with everything one needs for a longer stay and, even though the windows are large and can feel quite exposed, you get a lot of privacy by being below ground.
My only few small flags for visitors like us who came with heavy suitcases and were there to work during the day: there isn’t an elevator and the steps are steep outside the flat plus very narrow inside the flat, the wifi isn’t good enough to have video calls and the toilet is downstairs vs bedroom and shower room upstairs. But in general, if you’re using this as a hub and just visiting Paris, it’s perfect!