When 'Item' is set as a filter in the Criteria tab, the results will either only show the line entry of a transaction with the selected item or without that item. Notice that when this field is selected, the options available are either "any of" or "none of".
If "any of" is selected only the line entry for that item will show as result. If "none of" is selected all line entries without that item will show.
When 'Item On Any Line' is set as a filter in the Criteria tab, the results will show all other line entries on a transaction that has the selected item on it. There are five options to select from "any of", "all of", "none of", "not all of" and "is".
If "any of" or "all of" is selected they show results for all line entries with the transaction that has the selected item on it. While, if "none of" or "not all of" is selected they show results that do not include the selected item. Lastly, if "is" is selected this shows results of transactions that only has the selected item on it.
Note: There are also other filters on a saved search that when added will give different results even if the 'Item' or 'Item On Any Line' is chosen as a filter.