As with the set you can buy, I have no idea what is inside the boxes - only one of the technicians knows, and he isn't saying!
This video has given me some idea of how to use the boxes for more than a starter in a lesson. A colleague also suggested that the pupils could design further experiments to provide more evidence, for example, finding another one of the suggested object and weighing it to compare. I plan to at least give them to year 13 to have a play with at the start of a lesson, and they'll be great for that class where only half ever appear on time. I definitely want to have a go at a whole lesson, maybe with year 7, this week.