You may want to check the price differences between the BA coded flights and the one operated in the name of Kulula.com which is the low cost arm of Comair.

As an example, Kulula.com has both BA flights and its own flights listed. The flight we need JNB-CPT, cheapest BA coded is almost 1800 ZAR, Kulula's is 720 ZAR. So you are paying for those AS miles at a whopping price.

On top of that, folks in the Trip Advisor South Africa forum told me, if Kulula flight delayed they put people on the subsequent BA flights.

All the Comair routes have both BA flights and Kulula flights. The aircraft is the same. The prices have significant difference.