I would need to really understand your database and form design to be sure what is or isn't possible with each tool.
Multiple Insert will do an insert statement for multiple rows as displayed using the "repeat selection" server behavior
Multiple Updeate will execute an update for multiple rows displayed with a "repeat selection" server behavior from dataassist.
Manage relational table will delete records based on a key (ParentID) and insert multiple records based on a multiselect list or group of radio buttons. The effect is similar to an update but is actually achieved through a delete and insert. This is good for managing related tables in a three table database structure when fields from the first child already exist and you are inserting or updating the parent record.
Depending on your workflow, database structure, and what pages you use for what functionality it could be done a number of ways.
