Mathieu's apartment is a great place to stay in if you're in Barcelona; it is clean, eloquent and spacious, it has a big kitchen, and is ideally located in the city, a short walk from the major tourist attractions like las Ramblas.
Additionally, Mathieu is a great host; he is very friendly and helpful, and is easy to communicate with through Airbnb message & WhatsApp. The catalog he compiled with a list of recommended restaurants was particularly useful.
I would certainly choose to stay at Mathieu's place if I visit Barcelona again with my family or friends.