CellC is floundering a bit here. They don't really have any infrastructure that they can call their own, and tensions between Vodacom/MTN also doesn't help (including the huge amount of people complaining about coverage/connection issues)
With 8ta, at the very least, you know it's running on Telkom infrastructure. Even though MTN/Vodacom etc has to lease some of their hard-lines from Telkom, you know for a fact that the capacity 8ta has instantly overshadows that of what the bigger players have (and that's the reason why they opt to install their own fiber networks now)
8ta is here to stay IMO, and their data packages have been quite competitive. They're still young and have a lot to learn, but I'm sure a lot of folks are happy with what they're paying for an internet connection at the very least