We were fortunate enough to go in May as well, and it was the best money we spent the entire trip. Gumption did tell us about some of the people who had not respected the rules of the tour by taking photos of Necker guests and celebrities, and said it is the actions of people like this that might cause the end of the tours. In our group, there was one couple who clearly didn't care about anything they were told, they were taking photos inside the Great House minutes after being asked not to. We shamed them in front of the rest of the group and they stopped, but I'm sure this happens all the time.

Felix