Okay.
The experiment was conducted in New Zealand. The advantage is that people can try out a political mechanism that can be quite complex, depending on the choice made. When people try a system out, they make it their own and most of them, with the exception of new voters who were not familiar with the old system, are able to make a comparison.
In fact, if I have a choice between a referendum in advance and a ratification referendum after two general elections, I prefer people to be able to try the system out.