Welcome to FT,
outside!
Just because you visit places in Asia doesn't make it any more or less advantageous to buy your xONEx over there.
In regards to South Africa: The best way to look at things is to use the OW route map for rough planning:
http://www.innovata-llc.com/onw/default.asp?show=MAP
As you can see: You can go to a few places in southern Africa and to Mauritius from there. Otherwise, the OW Africa coverage is quite small. Be aware that there are some special rules in place for some Africa destinations.
Also, are you sure you want to credit to CX? This might or might not be the best program for your.