We have stayed in David's apartment for almost a week, and it was the best one of our Paris trips.
Location is perfect: 2 minutes walk to metro and Rue Rivoli. Just around the corner is Rue Rosiers - heart of Marais.
The aparment is clean, no dust at all. Fast wifi and decent shower. Kitchen corner, just enough to prepare a breakfast or simple dinner.
David itself is very nice man, easy-to-communicate. He even helped us to print e-tickets in his office, and deliver them himself, which was very generous of him.
To conclude: David's apartment is perfect for short stay in lower Marais, for one man or a couple. Highly recommended.