Christophe's apartment is absolutely wonderful. My husband, mother-in-law, and I visited at the end of November and chose the apartment for its spaciousness and lack of stairs (the apartment is on the ground floor). It had absolutely everything you could want; comfortable beds, two bathrooms with showers, a sizable living room and dining room, laundry, and a fully equipped kitchen. As a bonus, the apartment also has Netflix, which was a godsend when my mother-in-law twisted her ankle a few days into the trip and was couch-bound.
Regarding check-in: it was seamless. Isabelle, the caretaker, met us at the door. She does not speak English and I only speak minimal French, but we were able to get on just fine and she showed us how to unlock all the doors (the building is very secure) to ensure we wouldn't lock ourselves out. The apartment is also very close to the Passy train station, a pharmacy, grocery stores, and several restaurants. You can easily walk to the Eiffel Tower from there and, if you need one, catching a cab is very quick.
The last thing I want to note is that the apartment itself is beautiful. It is just as spacious as the pictures show and is extremely homey. I'd highly recommend staying there if your group includes 3-4 people. Thank you, Christophe and Isabelle!