If the main product has shipping or if another clicked checkout has shipping, double shipping costs will (of course) not be charged if another checkout with shipping costs is added. The respective checkout bargain (or all the different checkout bargains) does include the shipping costs, so it seems that you will have to pay shipping costs again for each checkout. That does not benefit the conversion. I would like shipping costs to be shown only if they are actually going to be charged extra when adding a checkout bargain.