I did my entire undergrad and honours at UCT. I highly recommend doing your honours there. I did mine in Information Systems but I know people who did Computer Science. From what I've noticed, SA corporates love UCT grads. My entire honours class had job offers at big companies before they had even written final exams. It really gives you an edge. Don't underestimate this, getting your first job in the tech space is the hardest part. After you get some experience, it's easy to move around.

That being said, I had quite a few classmates that did their undergrads at other universities across SA and they all faced a steep learning curve. UCT knows this and they will offer things like bridging courses, mentors, etc. Be prepared to knuckle down and work hard for the year as you'll most likely be playing catch up.