Great location in the heart of Paris, plenty of restaurants and supermarkets, and a huge mall at walking distance, access to public transportation (metro and bus) at less than 50 m.
House is spacious (compared to Paris' standards) and fits 3/4 easily. The 5 stories without elevator is not really an issue despite the fact that the stairs are steep and uneven (at moments - this is a building from the 19th century).
I would have given it a 5/5, however, I felt the whole experience was not as good as the one I've had with other Airbnb studios I've rented in Europe: there is a sweet Airbnb spot between a hotel (completely impersonal) and squat someone else's house (invasion of someone else's space). Unfortunately, everything feels like you're in someone else's apartment, from lotions in the bathroom to half eaten jar of Nutella and food in the fridge. If this doesn't bother you, this is a good value for money given all the advantages of this apartment and its location.