Most tourists avoid minibus taxis when in South Africa, if only because there is a learning curve involved and therefore they are not as user-friendly as taxis or city buses.
For example, in Johannesburg, there is a whole system of hand signals involved to “ask” a passing driver which direction their vehicle is headed, then there is another system involved in paying once you hop on board. Not to mention the chaos involved if you decide to get one at a busy taxi rank.
But if you’re the intrepid type, it could be worth learning the ropes, especially if you like to get to know the locals, and want to save a LOT of money — shared taxis are dirt cheap compared to private taxis, especially when you are going long distances (with the possible exception of Uber). But you have to balance price with convenience; minibus taxis don’t depart until they’re full, so if it’s an off-peak time, you may have to wait a while before you get going.
But what about road safety? Minibus taxi drivers have a reputation for driving recklessly, and the vehicles are not known to be in top condition, for the most part. That is a decision only you can make, but I will say that they have gotten a lot safer in the last 10 years.
And personal safety? Though many tourists fear the unknown, especially when the locals are a different color, race, or speak a different language, I have never heard of anyone being treated with anything but kindness by other riders. You may even get special treatment, as other passengers may see you as a curiosity!
For a lesson on how to ride a Joburg “kombi,” here’s a great article.
And for advice on minibus taxis in Cape Town, try this piece.