i stayed in nafsika and lionel's flat during a one month trip to paris and loved it! the flat is small but has everything you need to live comfortably (washing machine, dishwasher, TV, big closet, coffee maker, pots/pans). the bed is also super comfortable and can be converted from a twin into a double.
every day during my trip, i absolutely loved coming home and sometimes it was difficult to actually pry myself out of the flat. nafsika was very communicative during my trip, and checked in to make sure things were going ok. paris was in the midst of a massive heat wave when I was there, and she very kindly brought over a fan one day.
the flat is on the edge of the 11th and 20th arrondissements and is super convenient. i liked taking walks to belleville, marais, bastille, oberkampf, and to the nearby outdoor food markets. the metro station is only 2 blocks away. this is a working class neighborhood and there are plenty of grocery stores, cafés, and bakeries within walking distance.
the building itself is quite safe (2 keycodes are needed) and the flat is on the 3rd floor up a cute and well-worn spiral staircase. it is a typical parisian building with a courtyard, and sometimes noise from neighbors was audible but i did not mind.
i am hoping to come back to paris next year and would love to stay here again!