Hiya
One of the greatest dis-advantages of using a shark shield, is the false sense of security it gives you. I've done very stupid things, like diving in 3m viz. at Struisbaai, which is a KNOWN great white shark area, with my shark shield on. With the little more experience i've gained, i now realise how stupid that was. (To put it into perspective, i am PETRIFIED of Great Whites!!!)
The manufacturers warn you that shark shield isn't a 100% guarantee against a shark attack. I've heard stories, some claiming that the unit works exceptionally well, whilst i've heard the odd stories of the unit failing to protect the diver. If you have a great phobia of sharks, the Shark Shield is worth every cent, even if it is just for the peice of mind it gives you!!
My motto is now pretty simple, if the water is dirty, i don't dive. If there are ANY sharks around, (especially if they're mid-water or on the surface), i simply leave the area and find another reef.
Burleying whilst there are sharks around is looking for trouble. I've seen documentaries where sharks get into such a feeding frenzy, that one shark, even though it was bitten in half by another shark, kept on feeding!!! In situations like that, NOTHING will keep you safe if a shark has decided that you are food!!
At the end of the day, whether you're diving with or with-out a shark shield, let COMMON SENSE prevail!!
Regards
miles