I had the opportunity to stay for 2 nights with Valentina and Matthias. I didn't really get much opportunity to talk to Valentina, but Matthias was gracious enough to give me a walking tour of some of the sites in Paris, which was very helpful for my first time in the city.
The room was small, but ok. For me personally I didn't find the mattress very comfortable. The private bathroom was nice, but the layout is tight, if you have long legs you have to sit on the toilet on an angle or sideways.
I didn't have an issue with sharing the shower in their bedroom.
The area was convenient for me, close to Gare du Nord and the metro. However, I do agree there are many suspicious looking individuals who loiter in the street, especially late at night, it can be intimidating.