You're right, it's as if Vodacom don't want people to realise how this compares to the TopUp contracts that they are replacing!
I was called a month ago by a company called Mondo (if I recall correctly) and they wanted to see if I wanted to move over to a Flexi package from TopUp, to try for a month or 2 before I renewed my contract come upgrade time. Of course they told me that it is cheaper by 10c per minute. I see they failed to mention that there is now only a single flat rate and no off-peak rate!
Anyway, since I was interested in finding out as well, after much searching I found what you are looking for