We used Shuttle King for our airport-hotel transfers at JNB and as transportation from our hotel to the De Wildt Cheetah Centre.
We were underwhelmed by both drivers. I shudder at the thought of getting one of these drivers for a long term transfer between JNB and one of the lodges in the Kruger Park area. The driver who took us to the De Wildt Cheetah Centre got lost and I had to fire up Google Maps on my phone to bail him out. BTW this was my first trip to ZA so I had no local knowledge whatsoever.
It could be we were just unlucky with the drivers from Shuttle King. But personally I would be hesitant to book them for something bigger. And they are just about the highest reviewed transfer company on TA (and one of the more expensive as well), Who would I book as an alternative?