Review as of April 2018 - The location is the best part about this. A few minutes walk if even to Notre-Dame, the Seine, great French restaurants, the metro, etc. Communication with Corto was great. Very fast and responsive.
There are steep, small dark stairs leading up to the studio, after you take elevator up. Not a place for anyone that has issues with climbing stairs, especially with your luggage. No proper handle on the door which made it a bit odd to close. You basically have to hold onto a screw and pull hard.
The inside of the studio as of April 2018 is a bit cluttered with perhaps stuff left by other travelers and maybe it is used as an extra storage unit? I disagree with Corto's Space description which describes the interior architecture as "brand new." The photos need to be updated as there are different chairs that what was shown in the listing and there is added furniture like the sofa that sits on the ground.
The bed - The mattress sits directly on the ground, not elevated as it was shown in the listing. Not the most comfortable.
Bathroom - Shower pressure is very week and is small. Would not recommend for anyone over 6 feet. Also, the shower needs a good scrubbing.
Wifi - Strong wifi worked well.
TV - We did not have a chance to check out the TV.
The kitchen - Corto listed an electric kettle, but when I asked where he pointed to the pan to boil the water. So no electric kettle to make your tea or coffee.
The noise - Note that it is above a noisy street and you can hear people drinking at the restaurants nearby.
The loft needs a good cleaning, updated pictures and return to the original shape that the pictures in the listing portray.