If you print the label online, it should have delivery confirmation for free. Plus the price is cheaper if you're looking to save on a few cents/dollars. Only use flat rate boxes if you ship a box that will weigh a lot. Also, careful on the breather bags if you have corys or sharp finned fish. Corys like to gulp in air so breather bags are not that great for them. I've heard some shippers leave an air bubble for the corys but would rather just use poly bags.