I was staying in Paris for a week for an academic conference on the Condorcet campus (St. Denis). This was a nice accommodation for that, close to the metro (line 12), easy commute to Condorcet but also close to the city center.
Natasha and Hugo were very flexible with the check-in and check-out time, which was a great help, and they also responded very quickly to messages.
The apartment itself is nice; it's indeed on the 5th floor, but the floors are not that high so it's just the right amount of exercise :). It has everything one may need and some more.
The area is a bit hectic (meat market, fish market, crowds during the day), which can be a plus or minus depending on one's preferences. I felt sometimes a bit uneasy when walking home late at night, but then that may have been true in a lot of parts of Paris (I'm coming from a small college town).