When used internationally, it doesn't stop you going overdrawn! What it will do is to stop you going very much overdrawn (usually you can only go overdrawn by approximately the amount of the foreign usage charges).
Normal Visa is more widely accepted and I suspect much, much more widely accepted in SA, depending on where you are going. The major downside of Visa Electron is that it can't be used when the shop doesn't have an online authorisation facility, which is something to bear in mind if you are going off the beaten track.
It can actually be used online these days with most retailers.