In Belgium when you have a non-compete, you will get what is quoted in the contract. (Unless you start working for the competition)
It also depends on the job and will have a limited reasonable duration.
I had one, but unfortunately they annulled it when they fired me.(1) Otherwise I would have been given a year extra payment while working at a company in the same job, but not in the same field.
I know somebody who started working for the competition and in the identical job, but they just named the job differently. He never asked the money and the company never followed up on it.
I know of somebody else who was forced to leave their new job, but got the money. The law will side with the worker most of the time and unless there is a clear abuse of what is reasonable, then nobody actualy follows up on it.
If you get fired, most of the time it will be annulled and if people leave, they just go to somebody who is not the competitor.
All that said, if you are anything like a blue collor worker or an office serf, no way they could stick that to you. I sign them gladly and hope they forget when they fire me when they need to cut back.
(1)They gave me 5.5 months pay instead of the legal required 3, so that was nice.