Wow... wow... wow. What a gem this is. Like a boutique hotel in the perfect location, except with more space (and a kitchen, washer. etc). We loved our stay in Unit 21 (across the front of the building, with two bedrooms).
The beds ands linens were excellent. The bathrooms have all been remodeled and are very clean. The building sits above two restaurants (Nelson's is great btw). Being based in Les Halles is incredibly central. You are on the main metro station and can get anywhere.
In particular, we want to acknowledge the help of RACHEL! She was a warm smile every day when we came down the stairs. Always helpful and sweet. This is more than an Airbnb...
Two pro tips: 1) higher floors will be quieter. The restaurant noise is significant, but also a cool vibe. 2) when telling Taxis where to go, tell them Au Pied du Cochon (one of the restaurants below, that is very well known)