I've talked to a few people that have done it and everyone said it was worth doing once, but not the sort of thing you do twice.
Ask your guide's safety record. There's actually more problems with dive equipment than there is with the sharks/cages.
Keep your hands inside the ride at all times. There was a story about someone, in Australia I think, a few years ago - stuck their hand out and lost it.
Do NOT get in the water
Cape Town is cool
I've been a few times out of Gansbaai where Seal Island is located.(Shark Alley)... We have always used the Apex Predator with Capt. Brian Macfarlane. He runs a great operation and he will definitely put you on the sharks. Also do an early morning breach trip if you have the time... Awesome experience!
I don't think that you'll ever have to worry about me crowding your abalone areas.
Even with Firehuntfish's help, I still couldn't talk my wife into it!
As time goes by, my wife is very supportive of my desire to do anything that may be risky too.
The seals feed to the SW of the island at night and return back to the island in the cover of darkness just before first light. They seals travel in packs. The sharks will not attack the packs. However, the yearling seals are slower and 1/4 the size of an adult seal. They sometimes get left behind and come in solo. These are the seals that get blasted by the sharks. Normally, the sharks are about 10% - 20% successful on their airborne attacks. When I went in mid-July, 2014, the sharks were 8 for 8 batting 100% that morning. I think it may have been because of there was a moon directly overhead at first light giving the sharks better visibility of the seals above them earlier in the morning.
The trip left at about 6 AM in the dark and put us at Seal Island after a 20 -30 minute run at first light. Look for the birds (seagulls). The seagulls will see the strike first and will alert you to where the strike has occurred if you didn't see the airborne assault first. Most sharks I saw were 10-14 feet. One shark may have been near 16 feet.
I went with www.ultimate-animals.com It was a 36 foot catamaran with twin outboards. There are two other boats permitted to take these photographic/dive tank tours. All tours use the same size and style of boat. You can get on the roof (bridge) of each boat for a different viewpoint/photos.
Probably the most important thing I learned was that the boat I was on had regulators (compressed air source) for us while we were in the cage. The air tank stayed on the boat and three 20' air hoses attached to regulators came off the air tank. The cages are tied to the gunnel of the boat and remain there the entire time while anchored. Three people are in the cage at a time. You step overboard into the cage with your regulator in your mouth. You can stay underwater and look around for the sharks coming from behind, below or in front of you. One of the other boats did not have compressed air. You simply had to use a snorkel. I've dove for more than 25 years. Having to use a snorkel would have been ok, but not nearly as nice as having a regulator. The boat also supplied a full suit, booties, and a hood. The third boat was booked for a week with photographers and thus, I did not see if they use an air source or not. Both boats anchored about 100 yards away from each other at the SW corner of Seal Island. The sharks would go between the boats.
I got come decent pictures with some good canon gear and my Go Pro. I did not get a shark breach on camera. The only way to get that shot is if a shark hits the decoy being trolled, and we never got a strike on the decoy. The day consists of running to Seal Island in the darkness, looking for shark breaches for the first 30-45 minutes, trolling the decoy for about 30 minutes, trolling by the eastern side of the island to see the shallow area where the seals play in the water but the sharks do not attack them there because of the wave action and the shallow rocks that tear up the sharks, and then setting up the cage. The cage dive is the rest of the morning until about 11:30.
I would highly recommend going in the morning. Most, if not all of the breaching only occurs in the morning. You can see sharks in the afternoon, though normally fewer.
I'd highly recommend anyone considering it to do it. It is cool to see that sharks even if you don't get in the water. I've seen many bull sharks and some tiger sharks in my life, but the great whites are in a league of their own. The definitely got my attention!
It is not a given on seeing the sharks. I was fortunate and had great weather with light winds. The day before, was rough and they didn't see a shark until 11:30 in the morning, without a single breach.
Shark Week was filming there the week before I got there last year. (early July) I understand July is the height of the season. The sharks are only there for 3-4 months.
They were trying to get cage shark diving going off the Farallones, a group of islands about 13 miles off the San Francisco coast. They would have been chumming the sharks in. Divers (and others) put a quick stop to that plan. Can you imagine training sharks to associate an outboard engine with a meal? Any boat diver in contact with one of those sharks would know what (who's) for dinner. Makes me wonder about some of the places people surf in Safa. Not that sharks are rocket scientists of the animal kingdom, but still.
That video about the diver grabbing the sharks tennis ball sized eye to get out of it's mouth - wow! And the shark population is exploding along with the pinniped population off the west US coast.
Still, ab diving is another, beautiful world, and if you get hit by the landlord chances are you won't have to worry about growing old and senile in a retirement home.