Catherine's apartment was a very convenient location for our 6 days in Paris. There are two metro stops in easy walking distance: Kleber and Boissieres. There is a patisserie across the street, and several restaurants in the neighborhood. The Arc de Triomphe is a 15-minute walk in one direction, and the Trocadero is 10 minutes the opposite way.
The apartment is on the third floor, but has both steps and an elevator. There are four doors that must be unlocked before you finally arrive at the apartment - great security. The apartment is in a building built around 1900. The floors are wood, the ceilings are very high (3 meters plus). One shares the bathroom with monsieur and madame, but this was no problem. The bathroom has two sinks, a bathtub with a hand-held shower nozzle, but no stand-up shower. There is a wonderful towel drying rack. Monsieur showed us how to use the small washing machine, which did a great job on our sweaty garments.
The bedroom is medium-sized. There is a closet, a coat rack, a table, and two windows with small balconies (one offers a view of the tip of the Eiffel Tower!). The bed is comfortable but a bit small (we're used to a king-size bed at home). It would perhaps be great for newlyweds...
The kitchen is available for cooking or just having coffee and a snack. A space in the fridge was cleared so that we could keep a few groceries cool. We used it for cheeses and cream for our coffee.
Overall, we were very satisfied with our stay. It was convenient and comfortable. I recommend it highly, as long as you're okay with tight sleeping quarters.