The apartment itself was very spacious, modern and well decorated; comfortable with all the amenities needed to live there for extended stays (we stayed 4 nights).
The living room is on the street side, and that street in itself is quite busy - we heard traffic noise and sirens on a regular basis. That said, all the bedrooms are on the back side, and a very effective sound-blocking door is built-in to isolate the living space from the bedrooms. We closed that door before bed and the street noise magically disappeared.
There is a small grocery store next door with smiling staff, and the historic Brussels area is within about 20 minutes if you walk fast.
The apartment is located between two convenient train stations, Brussels Noord and Brussels Central. We arrived at Brussels Noord in the evening and walked to the apartment, which we wouldn't recommend as the area immediate to the station felt quite sketchy.
Serge was an outstanding host, very responsive and helpful.