We stayed in Xavier's lovely apartment with my girlfriend for 5 months while we were living in Brussels. Choosing that listing might have been one of the best decisions we have made! Xavier and his family living in the same building were very friendly, same for the neighbors renting the room next door. The room was located in a great neighborhood that had anything you might want close by and was even walking distance to the city center, very nicely decorated and furnished, the bathroom was spacious. The room was cleaned regularly and had any amenities you might need for long term stay. The little kitchenette was fine for everyday use and we were even allowed to use Xavier's own kitchen on occasion! Xavier was very quick to act on any problems we expressed or feedback we gave (e.g. providing extra chairs) and was very understanding and accommodating. If I was pressed to find something negative to say about the room , gun against my head, it would be that since it is top floor and there is no elevator you have to walk up a couple of staircases, but anyone would be a fool to let that impact their decision to stay there.
If I was staying in Brussels again, irrelevant of if it would be short or long term, I would contact Xavier in a heartbeat. Is the room available for the time you are going you should definitely do the same!