We didn't meet Jean-Marc, but instead his wife Elise. Their communication was fast and reliable, and they had no problems when we were running a few hours late due to missing a train. The apartment is small but cosy. The kitchen has all of the essentials. The shower is fantastic! Plenty of TV channels (not all that important, but it does help!) location is great - right next to a metro and just a few 100mtrs away from the Sacre Coeur and the heart of Montmartre. It is located in what I would call the Paris "red light district" so expect lots of flashing neons signs screaming sex - but the area still felt safe and welcoming.
The stairs are a bit of a hike, but you get used to it after the first day.
We had a lovely stay in the apartment and would recommend it :)