This apartment was exactly as described! Super comfortable and cozy and very clean. The location was awesome and just a 20 minute walk from Canal St. Martin, Le Marais, and about 30 minutes walk to the Louvre etc. Perfect location! I wasn't able to use the train because of the transit strikes but walking ended up being a perfect way to get around anyway. I stayed in the winter and it was quite warm and cozy with the heater and blankets provided, and check-in was extremely easy as access to the apartment is via a code, rather than a key.
Some things to note:
1) The apartment is in a fully enclosed courtyard that is not particularly pretty but does get a fair amount of light in the day time, so don't expect any pretty sights out the window.
2) The loft bed is quite firm (I thought it was very comfortable) and kind of a futon mattress, not a spring mattress, and the latter is a bit tricky to climb. This wouldn't be a good spot for people with mobility issues or anyone who needs a very soft mattress.
3) There can be some noise at night, between someone taking out the garbage cans around 9:30pm at night, neighbors in the building having parties, and a kind of squeaky weather-vane on the roof if it's windy. Gilian provides a little plug in fan in the cabinet in the loft, and that was enough white noise for me to be able to sleep without issue.
All of that said I had a lovely experience and would absolutely recommend this spot to future travelers.