Martin is a great host! The place is just like the pictures (even better!) we were a family of 4 (4.5, 1.5, mom and dad), and the places made our 4 week stay in Paris just awesome!
Martin gave us really good advice even before getting to the apartment to make our trip quite enjoyable, he also gave us a very detailed PDF with really nice locations nearby.
Extremely well located, with lots of light, and really good ventilation. Very close to the Metro, Parks, and tons of really nice restaurants and boulangeries.
The 4 floors without an elevator were no issue at all! The kids even had fun going up or down, if you are considering this, I would say, don't worry about it!