The apartment is quirky and comfortable (but smaller than it appears in the photos). We stayed there for 3 nights with our young children and we all felt at home (although we did have to keep a close eye on the kids on the stairs to the upper bedroom as they are open-sided).
The apartment building is very traditional, which made our stay feel very French/Parisian and less touristy.
The 87 steps up to the top floor apartment were a bit challenging after a long day! However, this didn't ruin our stay. And the view of the Eiffel Tower was worth it - this made my little girl's day!
Boris was incredibly helpful and responded almost immediately to all my messages/questions.