The location of this place really is amazing. 1 minute walk to the Metro station. We were in Paris during the public transport strikes so were unfortunately not able to use the Metros at all. However, Gare du Nord station is a 15 minute walk! We were also more than happy to spend our time exploring the Montmartre and Pigalle area - plenty to see and do.
The apartment is very small, but this is to be expected in Paris in such a wonderful area. It was very well heated and the building felt very safe. I would have liked to have known that the toilet was inside a cupboard inside the bedroom, quite separate from the bathroom. The bathroom is also especially tiny. However, apart from that, the space has everything you need. The location really makes up for any qualms you may have about the size/space.