We had a good stay at Elle and Sebastian's place. Sebastian met us at the door and carried up our luggage (there are a lot of steps - well over a 100). The flat was in an ideal location as it is a 5 minute walk from the Gare du Nord station (ideal if you are coming via the Eurostar).
The flat was very clean.
The only let down for this flat which nothing can really be done about is the noise. Paris is a very noisy city and there are sirens and drivers beeping all the time and this mean that often our sleep was interrupted.