I did calculations for my (failed) kickstarter campaign between Amazon Fulfillment and me personally packing and mailing everything.

Amazon Fulfillment would have cut my profit in half. Yes it saves you time but depending on where you live and where the fulfillment warehouse is, the size of the products you're making, and the cost of shipping them. For my specific case it wasn't worth it. Hiring a few neighbors and working out of the garage for a few days would be far more feasible.