I know that man catchers were invented sometime during the medieval times, but were they actually used during the medieval times?
The Gevangenpoort is one of the more important museums in The Netherlands. That means they wouldn't put man catchers on display if they weren't used. At least, they would comment if it was experimental or rarely used. No such signs, and the guides don't mention it. They showed the instrument and explained its usage.
It seemed a bit cumbersome to use to me, but recently I saw a Youtube clip in which the Thai police use man catchers to subdue a dangerous person: https://youtu.be/Hqtny9yj8u8. I haven't seen this in action, but it looks like standard equipment, the way it is handled in the clip.