I stayed at Pierre's for 3 weeks and I think this place is just fantastic. The apartment is located in a nice building on the 5th floor quite easy to reach by an elevator. Quite spacious for a Paris: "Chambre de Bonne", fully equipped kitchen (dish washer), bathroom, shower (petit), tv, wifi, speakers and a "clic clac" sofa bed. Neighbors are friendly and the general ambience is silent and secure. There is a good size window with an incredible view of Montmartre's Sacre Coeur.
Location is top. Close to many subway lines (Republique will take you anywhere), there is a park, drugstore, supermarket and many restaurants, bistros, cafes nearby (marché des enfants rouges is a 5 min walk). Parisian landmarks are also at walking distance: Pompidou, Notre Dame, Chatelet, Marais etc.

Pierre is a very friendly and responsive host who speaks english fluently. I'd definitely like to see me back at this Studio.