This is confusing, not sure if above answers the question 100%. That checkbox “Only once each duplicated key” is only useful if you have multiple duplicates (3 or more) for the same key. When you use this component, you can have your unique rows output to one pipe and any duplicates it finds also output to a different pipe. In that duplicates pipe, when there are more than one duplicate for the same key, this checkbox only sends the first duplicate to the duplicates pipe.