This is a fantastic little flat. It's very compact, just right for one person, but really well fitted out and the limited space is used well. The decor, appliances, and furnishings are high quality and the flat is stylish but comfortable. It was sparkling clean when I arrived. The location (between the Marais and the 5ème) is VERY central but also relatively quiet and calm—you couldn't really ask for better. There are plenty of tasteful and classy local restaurants and shops. The river is right there and the banks immediately around the flat are beautiful and really pleasurable to stroll along. The flat (and the area as a whole) are not the cheapest but if you have the money they are lovely.
M. Deroide was away and the check in and check out were administered by an agency. Check in was very professional and smooth, but check out was not so good. The agency worker was 25 minutes late, after having insisted that I get up early to meet her. She then went through a painstaking series of checks which not only took a long time but ended up feeling ridiculous—counting every single tea spoon, every plate, videoing every single appliance in operation. I understand that this is simply the procedure of the agency but it felt as though she was looking for an excuse to charge me extra. At one point she suggested that there should be more crockery (did she think I was trying to take it with me on the Eurostar?! That I had broken it?!) When I asked for clarification she quickly backed down and said that everything was in order.
Overall I would love to rent this flat again when M. Deroide is in town to take care of things (he was an efficient communicator and he also thoughtfully got in contact to suggest local restaurants etc)—but I would not want to deal with this agency again.