Gilles was very nice and helpful in the short period we met him. The apartment was exactly as described in the listing. You have to climb about 100 steps to reach the apartment. I'm sure this is common for most places in Paris without lift, but not scary like Amsterdam's stairs, i.e. steep and narrow.
The bed was very hard like sleeping on a concrete floor, no cushion at all.
Location was perfect, safe, and very central. Gilles' apartment faces the courtyard instead of the street so it is very quiet at all times we were there. Walking is possible to many major sites, like Notre Dame, Saint Chappelle, Pompidou, etc.