This is my perfect place to hole up and study when the apartment feels a bit too noisy and when I really need to be productive. You can stay all day, no judgement: there's a microwave to heat up your lunch, you can get food delivered, or just take as much as you want from the table full of plates of cookies, wafers, candy and meringues. They have a toaster too, and all the essentials to make yourself a peanut butter and jelly sandwich. Unlimited coffee, including lattes and cappuccinos (which aren't the best I've ever had, but do their job of caffeinating me), and a very large selection of teas. The staff is very friendly and helpful. They have all sorts of events planned and the first floor can get very noisy, so go to the second floor for silence and a nice view of the Place des Festivals.
Really worth it for a productive day!