The place was great! Me and my girlfriend stayed there for one week during midsummer and it was amazing!
The toilet was outside of the appartement but that was not a problem. There were as everyone else mentioned a lot of stairs but you get used to it after two days.
The place did not have an AC but if you keep the window open the room should be cool enough so that the stay is pleasant.
Apart from that we loved it and recommend it strongly for one or two people who seek out a cosy visit to Paris!