This apartment is small but a typical size for Paris. It has the basics you need for a short stay. We did find that it wasn't very clean and there were some ants. I reported this so I hope that the owner will resolve the issue. The ants weren't bad enough that we didn't want to stay just very annoying.
Our biggest problem was the beds. They do not have a true mattress but instead have a futon like 4-inch thick foam mattress that sits on a box springs very low to the ground. The foam doesn't really provide a cushion and every move on the bed you could feel the boards digging into your back and hips. This meant we didn't get very good rest for the time we were there.
The area near Gare Du Nord is a little seedy especially at night but we felt very safe in the apartment with the security it had in place. It is a short walking distance to Scared Ceour and to several cafes and restaurants. It was a great location to use the Metro and RER to travel to all the sights we wanted to see within about 30 minutes. Versailles was about 40 minutes by train and was excellent.
Overall if the beds and ants are addressed I would say this was the perfect place for us to stay. We are a family of 4 and were comfortable with the space for our 4 night stay.