The apartment was very central: it was easy to get to the nearest subway, easy to travel to and from the airports and it's basically walking distance from all the main touristic spots in Paris. The beds were extremely comfortable: we all slept like babies, which was very nice considering we were in Paris for a work event and were very tired when we got back home after the event!!
For us, the only problem was that it was a bit too hot and the heating was turned up all the way: we couldn't find a way to turn it down on our own, but we stayed in the apartment basically just for sleeping so it wasn't that big of a deal.
The check in and check out process were very easy and Merveil's team was extremely available to answer all of our questions.