My whole family live there, if you have good security in a decent part of joburg you will be fine.
They armed response unit are very very good. The only problem now is Zuma, lots of white south africans want out because they feel he may be the new Mugabi. Whether they are just paranoid or if this will turn into reality is unclear.
There are lots of very good private schools around the area where the standard is as good as or better than English education, the standard of live is very high and you will enjoy yourself on a UK salary.
If I got the chance I would, but bear in mind that when my parents had me they moved back to the UK because didn’t feel it was a good place to bring up a child.