Michel was very accommodating with check-in and out times. My husband and I were delayed on our way in so had to meet him a few hours later than originally planned, but he was really flexible about it. He also allowed us to check out at 6pm as we had an evening flight, which allowed us to make the most of our last day in Paris. He answered all our questions on arrival and was available if we had had any more during our stay.
The flat itself is fantastically located, but, as indicated by the pictures, is rather small. We stayed in mid-winter, but the heaters Michel provided were sufficient to keep the apartment warm. We found that the geyser ran out of hot water if we showered immediately after each other, but that may be less on an issue in summer.
Our main struggle was that the bed is very small - we had expected a double, but I suspect that is a 3/4 due to the space available and so it was very tight for two people. Also, sharing a 3/4 duvet between 2 people is tough. Again, that might be less of an issue in summer.
All in all though, we enjoyed our stay and being so close to the subway and main attractions on the Champs Elysées. We also enjoyed several of the restaurants located very nearby and would stay again for shorter-length stays.