Default Dynamic Preview Testing List
I offer a (3) suggestions for making dynamic preview testing easier:
It would be extremely efficient to just have the Bronto system automatically look for a default Dynamic Preview Testing list called, "Dynamic Preview Testing." Way more convenient than enabling contacts one at a time.
Just add a single checkbox option to toggle all users on any given list (when creating/editing a list) so that they are selected for Dynamic Preview Testing. Example:  Enable these contacts for use in dynamic preview testing.
When previewing, just pick a list from a dropdown. Could even be tied to user prefs so that it is always selected by default.