We stayed at Mathias place for almost a week. Starting with check in that was without a problem, all indications were sent by him and also gave us some advice on which was the best way to move around. when me get there (Saturday 21:30) the owner who lives on the next floor was waiting for us, and showed the place talk with us giving us lots of recommendations of what to do. Amazing lady =)
The place was really nice, was sparkling clean, big enough for us (a couple). There were a lot of things available for breakfast, some food, all you can need for cooking and eating, cleaning stuff, etc.
The only thing you should know is that the shower ceiling is a little low. I was barely touching it with my head while taking a shower (I'm 1.85 m).
All in all, was really good stay, location is perfect (subways 3 blocks away), Seine river is about 3 blocks away straight down the street where the apartment is.
I would highly recommend to stay at Mathias place. You wont regret it!