We stayed in this apartment for a week and it was a nice experience. The place is as described, very clean and cozy, and the location is superb, Ile St Louis is so charming and centrally located, but yet very quiet, with nice restaurants and shops around. The building is very nice, 1 block from metro station Pont Marie.
We had little trouble with the timer of the water heater, it turns off at 11 pm, but it doesn´t start automatically in the morning, so you should wake up everyday at 7 am in order to turn it on and be able to take a hot shower. However, we didn´t contact the owner for rhis issue, so maybe there was a way to modify it.
In conclusion, we recommend this apartment.