Sylvain's a great host. He communicates well, and helped answer all our questions. :) His place looks beautiful with all the plants and sunlight during the day, just like the pictures. We also liked the self check-in process, which helps you have a flexible schedule.
Location is away from central Paris, but is well connected. It is very close to the Goncourt metro station, which helped us get to all the places we wanted to see in 15-30 minutes.
Only minor negative would be the building entrance / passage, which is a bit smelly and unclean, but I don't think the host has much control over that.
Regarding the stairs (since I was worried about this before I made the booking), yes, it's a 2-floor climb (the room's in Floor 2, if you count the ground floor as Floor 0). However, you'll find stairs in most Parisian listings on Airbnb, and this place is definitely great value for money.
All-in-all, we had a great time in Paris and I would definitely recommend Sylvain's place for anyone looking!