The apartment is in a great location in Paris. We walked to every monument, museum and food hub, and only required the metro when travelling with suitcases. It is as described--a cosy space for two people, but the size seems standard for apartments around the city. There are a number of stairs, but don't let that deter you! Wonderful restaurants nearby.
My only issue was that the wifi connection was unreliable--however, it seemed to work much better in the morning than the evening, so that may be a "peak time" service issue.
In any case, Arnaud was incredibly quick replying to our messages, and organised a neighbour to help us check in when we were delayed arriving in Paris and couldn't meet Arnaud at our agreed time. Very helpful!
We enjoyed our two-week stay in Paris at Arnaud's apartment!