Actually, from what people write on the forum Openserve is probably the most stable FNO in the country.
The Openserve === Telkom is a bit of a misconception.
Yes, Openserve is technically owned by Telkom, but it's a completely separate company, ran differently, purely focussing on the infrastructure and don't deal with customers directly - that's why you have Afrihost to do that for you.
Personal experience:
Have fibre for exactly 11 months today.
100mbps/50mbps, Openserve, Afrihost.
I always get > 90mbps down and > 45 upload mbps on speed tests.
Had downtime once due to the aerial cable that was broken off outside our house by wild vervet monkeys (KZN), they fixed it in under 24 hours.
Sure local latency is a little higher than Vumatel for example (Openserve get 20ms between Durban and JHB, Vumatel gets around 14ms).
International it's pretty much the same and most depend on your ISP anyway.
Few months ago, we had a power outage in town that lasted 3 days and the Internet stayed up the whole time (we have solar panels + battery at home).
So anyway, I think you're being unnecessary fussy. There's no contracts, so it might be worth trying out.