The first contact between Mathis and us were very nice, everything was great, until we got to Paris. Since the first day we arrived in Paris it was very hard to contact him. We had questions about the check-in, because he wasn't there for the key exchange, but couldn't get him on the phone.
We made a few good first impressions of the apartment, but they turned bad very fast. First of all the good things: we were allowed to use his personal laptop, it has enough space for four grown ups and the kitchen was pretty nice and fully equipped. But then… there was a strange sour smell, always lurking in the floor, the carpet was dirty, there was a used tissue next to he bed, there was booger on a blanket, the dish washer had dirty dishes inside, we tried our best to keep the bathroom floor dry, as instructed in a manual he prepared, but it was a little bit challenging if you are not used to it. The bed and couch weren't comfortable at all and we accidently noticed that it was really really dirty under the couch.
As for the neighbourhood… The apartment is located almost directly next to a Super Market, which is nice. There is also a chinese cuisine and an african diner across the street. We researched the neighbourhood before we traveled to Paris and saw some bad impressions about it, being dangerous, but that wasn't the case at all, as far as we could tell, as we could walk around even by night without being harassed. But… the closer you got to the metro the more garbage was lying across the streets, there was also an increasing amount of hawkers, trying to sell fake sunglasses, debit cards and fake train tickets. For us it was okay, but we wouldn't really recommend it to families with children.
There were too many things that were wrong with the apartment, personally we wouldn't recommend it at all if you want a comfortable and clean place you gladly want to return to at night.