I thoroughly enjoyed my stay in Gilles's flat and recommend it highly. I would certainly come back here on my next trip.
The place came as advertised: small but with all of the advertised amenities and an incredible location in the Marais. The size of the apartment did not bother me at all as a solo traveler and access to the Marais, which is a great neighborhood from which it is easy to get to around on foot or via the metro, cannot be beat. Just keep in mind that the studio is up six flights of stairs - something that should really be considered if mobility is an issue.
Gilles himself was a very good host. He did not respond to my messages regarding check-in right away, but gave thorough instructions when he did get back to me. He was fairly hands-off, but I imagine he would have been very helpful had I asked for more guidance. Potential travelers should be aware that Gilles will pop into the unit during the day while you are out. He was very respectful of my belongings, but those who are concerned about privacy should treat the unit like a spare bedroom in the host's apartment rather than an empty apartment. This is hardly an uncommon set-up on AirBnB so should not be of any real concern.