So... the Multiplier was offered to me as part of an award ticked. after you book an award or revenue ticket, you can go back and buy extra miles. they have nothing to do with the travel itself. it specifically says that the miles have nothing to do with your trip, and if you end up canceling your trip the miles would still post.
For me it was a no brainer. needed 1,200 miles for another reward ticket, to purchase miles would cost me $100 (processing fees included) and to "buy" them using the Multiplier was a flat $48. Win win...