Re: entering SA on your SA passport. I think that puts you at the mercy of the local government in the event of a natural disaster or civil unrest, i.e. you’re ****ed. If you go in on your UK passport, you can just make your way to the UK embassy for swift repatriation.
Of course, you can’t legally enter SA on a foreign passport as an SA citizen, UNLESS the your place of birth on the UK passport shows somewhere other than SA. Seen a few threads online from SA citizens having no issues entering SA with UK passports because their place of birth was somewhere like Swakopmund or Harare.