What is the real issue of not handing your line over to the isp. if there is problems then surely the isp have to interact with telkom to sort out the problem. you paying them so they must provide the service. i simply cannot understand what the big deal is.
Ok. So you move your line to your ISP and maybe save a few rands. Then you decide (for whatever reason) you no longer want to use that ISP. Now what? You can't just pay for the line so you need to either move your line (again) to whichever ISP you're moving onto (if they offer it) or back to Telkom.
It's fine if it's an established ISP with a good reputation or at least one you've trusted for a while. It's a bit risky moving your line to an ISP that hasn't been around all that long.
Just avoid IS at the moment. For your stated needs Mweb would be fine, as would the others. Comes down to price mostly.