Generally, this is a nice place; location is great, near Rue Montorgueil communication is smooth with L, and it's on the first floor (which in France usually means walking up one flight). The place has a countercultural vibe which was interesting. I would recommend for most people.

If you are, however, extra sensitive to noise and need it to be quiet in order to sleep, I would recommend searching elsewhere.
What I write below ONLY applies to noise sensitive people. And I only write it because the place is advertised as "very quiet", as of the time of this review, which was actually why I booked it.

First, the heater makes an sound every few minutes, sort of like a spinning sound then a bump, like something dropping inside. It probably won't bother most people, but to be honest, it bothered me a bit. If you turn it off, there's no more sound, and when I asked L if I could get a small portable heater, he did agree to contribute to the expense. L is a reasonable host who tries to make the stay work for guests.

But more an issue for me was late at night, the sounds of neighbors could be heard clearly. I was startled awake in the middle of the night by noises from upstairs, and after a few minutes, I saw in the courtyard that someone was pushing the light switch on-off several times, and I could actually hear the sound of the button pushing through the ceiling.

Long story short, I moved out after one night, so it could be that my situation was only for that night. I only had a few nights left in my Paris stay, so I accepted the financial loss and found another place. I did mention in an e-mail requesting L to consider adjusting the check-out date so that I could get a partial refund. He responded to the e-mail as a whole, but did not respond to this specific request. I left the situation at that.

So in summary; if you're generally okay with a moderate level of noise, go ahead and book the place. It's quite nice in other aspects. But if having a really quiet place is a priority for you, check out my other reviews.