The flat is located in the 3rd arrondissement on the Boulevard Saint-Martin, just near the Porte Saint-Martin and Rue Saint-Martin. There's a metro station Strasbourg-Saint-Denis (lines 4, 8 and 9) and plenty of bus stops nearby. It is also in the walking distance from the République square and even (if you do not mind 20-30 min walk through the streets) Ile de la Cité and Gare du Nord. So, I´d say, the location is quite convenient for an average tourist, arriving from the CDG airport.
There are also plenty of dining places and supermarkets around (Monoprix, Carrefour, etc.).
Inside the flat there had been everything we needed for our stay: a fully stocked kitchen with all kitchenware, a shower, a place to store our clothes, towels, clean bed sheets, etc. Ariane even left us some bread and jams so we could cook ourselves a breakfast right away :)
Note, though, that the balcony of the flat is facing Boulevard Saint-Martin, which is quite noisy during both the day and the night.
We were visiting Paris in the days of extreme warmth, which meant that we had to keep balcony opened (since there's no air conditioning in the flat), which were a bit annoying.
But in the end, if I´ll come to Paris in the future, I would definitely choose this place again.