The apartment is very central and easy to access from Gare du Nord. It's walking distance to the Canal st. Martin and by taking the metro at Republique you can get anywhere else very easily. As others have mentioned it's at the top of the building with no elevator so be prepared to climb a bit. The street is pretty quiet at night with no loud bars or restaurants at ground level.
Bruno was very helpful by arranging an early check-in and
provided consistent and fast communication. He offered a few basic kitchen implements and amenities like coffee/tea so it's easy to cook or take meals at home if you want.
The only unusual things I would mention are that the stairs can become very dark at night (even during the day) and the lighting was never on. I wasn't sure if the little buttons near everyone's doors were to turn on the lights, or were doorbells, so I never tried using them because I didn't want to ring anyone. I should have asked Bruno about this. In the US the hallway lights are always on. But I just used the light on my iphone and it was fine.
Also, I visited in early summer and even on a 75 degree day it sometimes got kind of stuffy up there. I didn't see a fan (or ask for one) but I found that by opening the apartment door it would cool down quickly from the air circulating in the hallway.
Overall a cozy & central base to explore Paris from!