yes its the baitrunner feature and adjusts the drag setting when in bait runner mode.

Baitrunner mode is switched on and off using the black and red lever just above the dial/knob.

The baitrunner mode allows you to have one setting which allows the fish to run and take line once it has taken the bait. Then either flick the reel out of bait runner (can do it using the lever but more commonly performed by turning the reel handle which puts the reel in to gear) and you then fight the fish using your normal drag as preset using the drag adjusting knob at the top of the reel.

The dial you are querying therefore adjusts the amount of resistance when the fish initially takes the line. But you will only be able to see the effect of it on the spool when the red and black lever is in the forward or up position ie baitrunner engaged.

This feature is really good when either strayline fishing or even livebaiting. If you dont want to use it then you can just fish the reel like normal

Btw, I have a spare spool for that reel if you are interested.

Yeah I have used the kilwell version of that reel which is pretty much the same and found them great value. Landed a 26kg kingi on it about 6 years ago and the reel still fishes very well and has landed a number of smaller kings and a fair few decent snappes off the rocks too.

20kg nylon is probably overkill. I have a few spools for mine and have used it for 6kg, 8kg, 10kg and 15kg. Would recommend 10kg as a good all round line to use.

Have never used jigs with it. Only straylined and livebaited really

$10 for the spare spool plus postage to get to you I guess unless you want to pick up from the north shore. Its not new by any means but always good to have a 2nd to spool up with a lighter or heavier line

If you want to use jigs you would ideally want a faster retrieving reel than the silstar, but no harm trying it out. If you use jigs you base it on the depth of the water, 50g = 50feet, 100g = 100feet and so on.