Superb. I stayed there for 6 weeks while looking for a permanent apartment in Brussels, and I cannot recommend it highly enough — particularly for long-term stays.
The location is great because it's located in a very quiet street, but within 3 minutes you can be at the heart of life in Brussels. Being the top floor, there are no noises from neighbours, and no need to worry about the church opposite the apartment because they don't toll the bells.
The apartment has everything you can possibly need, from cooking utensils & basics like oil, to excellent internet. Besides, it's full of charm & cozy: you feel at home the moment you set foot in it.
The only thing to know is that it's a 3rd floor without elevator. It was no problem for me, but people with mobility issues or who are carrying heavy luggage can find it challenging.
Having said that, I would have no doubt whatsoever in returning to it, or recommending it to friends & family when they come visit — I'm sure they'd love it!