As other reviews have mentioned, this is a very spacious apartment in a great location. It is decorated in modern Ikea. There are a few quirks that travelers should know about. For one, there are three bathrooms, but the one on the lower level does not have a toilet, so you need to go up a flight of stairs to use one. One of the bathrooms on the upper level does not have a shower curtain so could only be used for a bath, despite having a shower head attachment. There was ample hot water and great water pressure.
As mentioned by others, there are a lot of stairs, especially to the upper level which has three bedrooms. There are no handrails. The bedrooms are spacious and the beds are comfortable. There was a frequent rumbling sound that could be heard in bedroom on the lower level , which I think might have been coming from the trains entering the nearby Metro station. It didn't bother us, but might be a problem for a light sleeper.
Despite these minor inconveniences, we thoroughly enjoyed our stay at Jean Jacques place and would recommended it if you need a large place to stay while visiting Paris.