My wife and I travelled on the Gautrain, twice, to and from JHB airport and Centurion. It was quick and the wait was not more than 10 mins for the connecting train from Marlboro.
The downside is, it is pricey but then subtract your fuel- and parking costs as well as the inconvenience and it will probably turn out to be a "bargain". Not a luxury for everyday use, though, unless you are sponsored but it does save one the drive in traffic and having to locate suitable parking.
One area that needs attention is the parking at the stations as it seems it was totally underestimated and one "struggles" to find parking. This was a particular problem at Centurion station.
Beware that if you have large baggage that there is limited space here for and you may have to stand to hold it.
An enjoyable and swift experience nevertheless.
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