I've hitched into Brussels from here a couple of times. Can save you the ridiculous price of the train to the center. (The other option is bus #12 but it's not great if you're going to the center or to the west of the city.)
I hitchhiked many times from this spot. The left side is the best side. Right after, or before, the first traffic light. It seems there's no space to pull over, but Belgian people actually can. All the time.
When I was there there was almost no traffic. The little traffic that was there was quite stuck up (EU bureaucrat type). Finally a bunch of cool German kids in a van stopped. I never went back to this spot.