Have to agree with Rodent, but let me be more Verbose.
Sentech is an option if you are looking to do some light browsing and occasinally download something. I have a friend who is very happy with the service. But he is a very light Internet user. He doesn't care about his latency, not does he have a clue about what a kilobit or a kilobyte is. So for him saving R250 or so by using Sentech instead of ADSL makes sense. Of course by saving R250 he loses decent latency, speed, stability and semi-competent support. Oh and shaping, MyWireless is supposedly (probably) unshaped. That can have a big effect on some things like MMORPGs. MyWireless was great for MMORPGs in the beginning, but they haven't really been playable for a good few months now.
Anyone who wants to use the Internet for anything more should really rather look at ADSL. If it wasn't for the cap on ADSL it would be a total no brainer. It's a little more expensive than the 128k package and provides a vastly better service (right until it stops). After you hit your 3gb cap you can buy new increments of 3gb from most providers for about R230. I personally never went over 6gb, but then I don't try download the Internet. If you really wanted to you could probably hit 6gb in a week fairly easily.
I think a MAJOR difference is also that ADSL has no contract. My recent experience has convinced me for evermore that having no contract is worth real money. If it weren't for the contract I (and I suspect many others) would have dropped Sentech months ago. If MyWireless had no contract I would be happy to try it out again in a couple of months. But alas, this is not the case.
(*** suggestion to Sentech, offer a monthly option. You may be able to win back a bunch of customers later once you have fixed things ***)
In summary, the guys who like Sentech seem to have price as the most important factor. I personally think performance is also very important. The fact of the matter is that Internet Access in SA is expensive. I not right, it's not fair etc, but thats the reality. My experience with Sentech reminds me of the old saying. If it looks too good to be true, it probably is.
Good Luck,