We are widely travelled globally and have used Viator many times, including private tours, quite happily. We were stunned at the apparent lack of attention to us and our location/participation/understanding of where to go and what to do by our guide Enrique. Whenever we were in a confusing situation such as in a queue for example,which way to go since we do not understand Spanish or what was or was not included in our tour notwithstanding the written descriptions he was nowhere to be found. In summary it would have been only a little more confusing but a heck of a lot cheaper if we had just hired a taxi and took our chances. Save your money! Do not use this tour.
It was the worst private tour we have ever experienced in all of our travels to more than 44 countries. Unfortunately I am required to rate this as 1 star. If there were a category for negative stars that is how I would rate it.

Our guide and driver picked us up from the Sheraton inside the park on the Argentina side, transported us across the border into Brazil, and facilitated the immigration process. They were flexible in allowing us to take an unplanned helicopter tour of the falls. Our guide provided helpful information and allowed us to spend as much time as we wanted at each of the viewpoints for the falls. After we had lunch, she helped us get postcards and postage. I would highly recommend this private tour.

Our tour guide Gustavo A. picked us up from our hotel. He told us about the things we were looking at and the places we would see. We had been to the Brazilian side and so he changed his plans to meet our needs.

lovely. Our guide was very informative and Friendly. The falls were spectaculat. They should be on everyone's bucket list.