The experience was terrible. I checked in quickly on the day, dropped my luggage and then came back late at night only to find myselt locked outside of the hotel with no night staff on duty to let me in. I tried ringing the bell, calling the phone number and loudly knocking on the door for several minutes without any success. I then tried to book another concurrent hotel next door (where the night staff was really responsive and made best efforts to be helpful) but unfortunately they were full. I then got back to Paris Art Hôtel Quartier Latin, tried again the bell+phone+knocking to no avail. I went to a second hotel next door, also complete despite a nice night staff. Came back, did the bell+phone+knocking at Paris Art Hôtel Quartier Latin again, and to no avail again. I then repeated the process with a third hotel (complete again) and back to Paris Art Hôtel Quartier Latin. The third time only I think my very loud knocking made the night staff come and open to me. While he was polite, I didn't felt he was really apologetic and tried to blame the bell and phone being broken. The whole story took a bit more than half an hour in the middle of the night. Not a fun one.
On the second day when I got back at night (a bit less late than the first day), another night staff was there. She opened me but then my electronic room key wasn't working. The night staff had to come wiht me with a pass.
On the morning after the second night, at 08:30am, a cleaning staff entered in the room without knocking.
Also, the bathroom had a slight sewer odour.
So even if the hotel itself is nice and well located I can only advice to book another nearby stay.