I walked up it about 10 years ago (Platteklip Gorge) - straightforward walk no need to get a company. We walked up, joined the rest of our friends and got the cable car down with them.
I also walked up Platteklip Gorge, back in the mid '80's, and like you say it's pretty straightforward, as I recall. We didn't use a company either, but we did have a local guy with us who knew the mountain very well. Took the cable car down.
Fantastic views of the whole peninsular as you walk around the plateau, so long as "the tablecloth" is not laid.