I agree with all the positive comments by other visitors, and the pictures are fairly accurate, although they make the apartment look bigger. Since people typically have the tendency to bias towards the positive and overlook the negative, this review will focus only in the negative, so you can make a more informed decision.
1) The stairs: 105 steps, including 5 inside the apartment. Yes, it is nice to end the day with some excercise, but after two or three I was kind of sick of them.
2) Communication with the host is minimum and difficult. Expect to be in limbo until 5 o 10 minutes before arrival and departure and if you have any problem during your stay, you are on your own. If you expect some kind of social interaction with the host to enlighten your experience, then look elsewhere.
3) Unflexibility in terms of arrival and departure time. Look at the terms, if you leave early then the hosts charges a ridicoulous expensive fee for no reason.
4) The light. There is a huge window in the roof. If you travel in the summer expect to be walken up at 6AM with the bright light of the morning in your face.
5) There is a laundry machine but there is no laundry detergent.
6) The dimensions. The flat is tiny, maybe 150 sq ft. If you are taller than 5.10 then you will find your head scratching the slanted wall quite often.