the most important thing to do is read the label...are there no local south african brands of cat food that might be good for your kitty?
My Australian friends feed their cats kangaroo meat (giant bouncing mice, as Sylvester called them.) All the brands you mention are from the USA.
As long as cat food does not list filler as major ingredients it should be all right. Watch for meat=good
corn, wheat, peas, byproducts in the first three ingredients=bad.
My vet prescribed Rabbit and Pea Royal Canin special diet for Gizmo. I switched her to something better (also rabbit) when the label showed me that the food was more like Pea and Rabbit. The protein level was too low for my liking.
The Royal Canin sold in the shops is a little different, and as I said it's better than Science Diet and Iams, but I'd still look for local products with high meat content.