We have a great time in Paris. The apartment is just as you see in photos. We didn't meet Mathieu but he arrange with Pierre and everything was great with him.
Is a second floor by stairs but that isn't much trouble.
The Internet connection was very good!
We didn't like the neighborhood so much, but it's in a good location near Saint Martin and has a metro station 3 blocks away, that let's you in Montmartre or Champs Elysee (Triumph Arc) in a few minutes.
We recommended to Mathieu, if possible, to make a little space for the clothes and stuff of the guests. The same with the kitchen. If you are staying like us for a week you like to settle down with more space for your things.