The Analytics Suite Delta is based on our new data factory that allows you to take advantage of all analyses with a "Unique Visitors" scope.
As you will have understood, you will be able to make a noticeable difference between our old data factory and our new Delta data factory for this "Visitors" metric.
This is simply because in our new data factory we are now using only unique visitors, so the "Visitors" metric in Delta is indeed the equivalent of Unique Visitors in the Analytics Suite 2.
All the tools in the Analytics Suite Delta are using this notion of "Visitors" (i.e. "Unique Visitors") by default.
You can find a detailed explanation about this in this article in our Help Centre:
You can also find all the changes that have been made to our metrics in this article: