I found Mona's place while looking for a 3-night stay in Paris during December.
Overall it was an OK, you-get-what-you-pay-for type of apartment where you can save a little money in an already expensive city like Paris.
Just, a little more cleaning wouldn't have hurt.
Some specifics about the location:
A friend of mine who lives in Paris suggested the 11th arrondissement as a nice, well-connected and safe zone for tourists. However, not every corner of the 11th arr. looks exactly the same.
While Mona's place is, indeed, well-connected to most of Paris through public transport (we mostly used the two metro lines, 2 and 11, available within less than a 5-minute walk), it isn't exactly located in a safe zone.
We had to select the streets we crossed in order to feel safe and protected while returning home at night. The neighbourhood isn't exactly lively, and for the most part, people you cross on the street isn't the type of people I would feel secure to have a friendly conversation with