When you cast out to a sandy bottom the sinker's prongs dig in the sand and helps it stay there. Good for on the beach as the surf wont hopefully move your line etc out of the hole your fishing.

When its time to check bait or reel in your dinner, you apply enough pressure for the prongs to flick back, it releases it making it easy to to bring in. Once you have the sinker back you flick back to orginal postion to cast out again.

I like using them anyway off the rocks when i need a sinker of that size. i have found the prongs assist in not logding in reefs etc. I mostly strayline of rocks how ever. Also if you dont have  anything and wanting to rebait, the faster you reel back in lifts the line clsoer to the surface avoiding snags.

in the past at harbour bridge spot i just overhead cast and use a pully rig and we have been successful. About 4 ounce or 5 ounce sinkers are fine and preety much good for most places

Thanks for your info guys, will go down to Top Catch and get myself some of those bos breakaways. As long it they dont snag every couple of minutes I'm happy with them - the snagging problem had costed me so many sinkers and hooks apparently...

I hate it when HnF use crappy thin wire for there sinkers, essp the bos's, they are so thin in wire they pull out in a moderate current and wont hold wet noodles. i asked them to change the wire to make it thicker and some where along the line they did just that.. :) now they are all good on beaches, i always use a running rig, as the trace on the 90 mile wraps it's self around the sinker line where i fish in matata...