We really liked Sylvains apartment. The location is great, walking distance from Gare de l'Est and Gare du Nord. It is also very near line 7 on the metro, and there are alot of good dining options nearby.
The weather was rather cool during our stay in mid/late June, so temteratures were pleasant. However, the lack of an air conditioner will make higher temperatures an issue.
The bed was comfortable for two of us, however the futon couch was not very good for a nights sleep. The coffee maker was great to have in the morning!
In all, we would recommend this apartment for a couple not minding the lack of an AC (or going to Paris when temperatures are pleasant).