Alexandre was the perfect host, me and a friend arrived quite late, 10pm, but he would wait for us and then take the time to recommend places - and such to avoid, help us plan our stay and even checked in during our stay via text to make sure the heating was working.
The flat: Concerning the smell: Yes, you can tell that people smoked in the flat before but it wasn't disturbing at all (and I don't smoke). More importantly, the flat was super clean, the interior very cool and smart as seen on the pics. Also, a very comfortable 140cm bed.
The area: The flat is on a very lively street with lots of nice bars (but you don't hear the noise as you are on the 5th floor, facing the back). It's also perfectly located to discover the city by walking as you cross lots of sights while you make your way towards the Seine.
Would always go back and can fully recommend!