It can be seen why Jill ferrets are popular as working ferrets. Their size enables them to pass with ease through the net, and so they are less likely to disturb the net. White ferrets are popular as they are more easily seen by the owner.
The bottom picture shows how a large Hob ferret (Charlie) would unset the nets.
Fred explained to me how hobs are used to drive rabbits from holes to shot with guns or caught using dogs rather than trapped in nets.

Entering a burrow.