We rented the apartment in late April. We were visiting Brussels for 9 days, with the main purpose being to attend a cousin's weeding. It worked out well for the 6 of us: our family of 4 (one teenager, one 2 yr old) and my wife's parents. A pack-n-play (portable bed) was provided - it was great we did not have to transport/buy one. Ideal location for us and very quiet. The weather happened to be amazingly warm that week so we took full advantage of the terrace and garden area.
This is a great place to stay if you want to be in the Forest area. Within a few blocks is the park and transit. And for us, the apartment was only 10 mins. walk from our cousins house.
The apartment is older and some of the doors are difficult to close - but it didn't really impact the experience for us. One thing to note: 2 bedrooms are connected together with french doors and the bathroom is through the 2nd one - it works ok for a family, but it would probably be awkward for 3 couples, for example.