These are designed as a direct response to the growing number of fisheries that insist on inline feeders, with issues of fish welfare.
As the mainline runs through the feeder via a tube, any breakage which occurs above the feeder means the line pulls through and fish are never tethered.
Rigging the feeders like this provides the easiest way of using a very short hooklength in order to place a hookbait right next to the feeder. This can be very effective for Carp, Bream and Tench on stillwaters or big Barbel on rivers.