Forgot to say -
It's best to book to fly soon after you arrive in Cape Town so you've got a chance of an alternate day if the weather's bad on the booked day.
Warning: They want full payment at time of booking but, if the flight can't take place at all because of weather, only refund you 80%!
20% of ten grand is a lot to lose.
I suppose they've got so much demand, they can get away with it.