I stay a whole week in this apartment. It is small but spacious enough for two people. The surrounding is nice with a lot of bars, bistros and restaurants. I am a woman travelling alone, and walking the streets when coming home at night is absolutely safe.
Yes, you can hear the metro, but it's really not a big deal, and I am very sensitive when it comes to sleep. Don't even worry about it. The staircase is louder when people pass by, but in general it's a very quiet house.
The metro stations of the line 3 and 11 are close by (10 min by foot) and there are aswell several bus lines. So to go to the center of Paris will take you 30 minutes, which is a good time for Paris.
The apartment is well equipped for a vacation stay. I worked from there and for me the internet connection was good enough for that.
I really enjoyed my stay here and can absolutely recommend it to other travellers. For people who look for long term stays it might be a bit dark (first floor with windows into the court yard of a building with 6 or 7 stories, so you don't have direct sunlight in there).