The set up of the jig hook and extension puts the tow point 15mm back along the fly so that a medium to fast strip will cause the fly to dart off in different directions much like wounded or fleeing fish. The 15mm of 8mm diameter closed cell foam tube above the hook eye give the fly neutral buoyancy so then when you pause the lure it basically suspends at or close to the level it was being retrieved giving predators time to attack.
A great fly for barra and mangrove jack ... put a good cast into the target area and to allow the fly to settle for a few seconds before doing tiny twitches of the rod tip to cause some rings on the surface suggesting it's a natural struggling and then if that doesn't induce a strike to commence either a slow roly poly retrieve, or a series of stop start strips, back to the boat or bank. Whatever the retrieve the occasional pause followed by some twitches of the rod tip area good idea.