I could not run out of great things to say about my stay! I have not a single complaint about the apartment, which was spacious, secure, charming, comfortable, and full of amenities that are difficult to find in Paris, such as A/C, a dishwasher, and washer/dryer. Also, it's up just one small flight of stairs, which was a blessing (as most of colleague's stayed in similar old buildings with many stairs and no elevators). I stayed in Paris for four weeks and it truly felt as comfortable and useful as my home apartment. My favorite thing to do every morning was to open the giant windows that look out into the inner walkways of the building and drink my coffee.
Christian is an excellent and thoughtful host and I greatly appreciated the house guide and neighborhood guide he prepared for guests, which I referenced every day. He also responded to messages very quickly, and the check in/out process was seamless.
The apartment is also ideally located because it is right next to a couple bus stops and the metro - my work took me all over the city but I never felt inconvenienced by it due to the quick walk to public transit. Also, it's located in a mostly pedestrian enclave that's full of both sit down and quick stop eateries - it's busy, but if you're feeling lazy there's dozens of options for guests with just 30 seconds to a few minutes of walking.
I think anyone who manages to secure a booking here would be very lucky, I certainly hope I'm able to book again if I return again for work next year. Thank you Christian!