The apartment was beautiful. It's small but perfectly formed- it's really homely with Pierre's collection of dozens of lights giving it a very warm feel. It was equipped with everything we needed. We were only there for a couple of days but could have gladly stayed there much longer without feeling claustrophobic as it's so bright and airy. It has a proper bed which was very welcome. The shower was powerful and hot. There was coffee in the fridge. The shutters opened out onto a quiet street with a view of the top of the Sacre Coeur.
Pierre was a great host, replying to all queries within minutes. He was happy to advise on the local area such as where to find the best boulangerie. He didn't mind waiting for us to arrive later around 23:00 after showing us everything in the flat just left us to it. His English was great (which was lucky because our French was not so good).
The area itself is lovely, about 15 minutes' walk from Gare du Nord, 5 minutes from Sacre Coeur. There are plenty of bars, restaurants and shops nearby. It was close enough to public transport that we didn't take more than half an hour to get anywhere we wanted to.
If you're looking for somewhere to stay in Paris then I couldn't recommend it enough. We'll definitely be hoping to stay here next time we're over!