I am giving them a two because you really need to be aware of their tour operators. I was scheduled for a boat ride to Robben Island but the tour was cancelled due to high wind.
When I called the tour operator they said that they do not give refunds and I had to call Viator for help. Well, they did help but we shall see what kind of a refund I get. My tour was just short $100 and included a city tour too. I did not take that since all I wanted was the tour to Robben Island.
Just be careful. If I had booked directly with Robben Island, I would have been refunded or rescheduled, as were many people that I saw in line today.