The host is great, and he replied to all my questions in few minutes.
Concerning the apartment, it is placed in a very "strategic" location since the RER B and bus stops are very very close, so it is possible to reach places like Notre Dame or Montparnasse in few minutes (or in 10 minutes by walk).
The apartment is ok for 2/3 guests, and it has all the useful stuffs for short and long journeys.