This Traboule apartment is certainly unique! We stayed two nights, with our 16yo on the sofa bed, and we were fairly comfortable. I would not recommend the apartment for four people as it is very small and the bathroom is accessed through the master bedroom (which does not have privacy curtains on the dividing glass). The toilet room opens immediately into the kitchen/living space, something to be aware of if that kind of thing matters to you.
The descriptions are clear that this small apartment has no direct light, as the windows open onto the traboule lightwell (small courtyard with the sky far above) - we did find it stuffy, and had to decide between the chance of overnight noise with the windows open, or no fresh air with the windows closed. There was not much noise overnight when we stayed in September.

Location is in the heart of the historical centre - very charming!
Amelie was a very responsive contact for our booking, and when I had trouble with the key safe it was great to be able to call the number provided and speak to someone (in English) to help me on the spot.