Suppose your customer rejects the package. The package will be returned to Amazon warehouse. It is possible that your glasses got damaged while in transit but no one at Amazon warehouse will check them for damage by opening the package. Now these glasses will be again shipped and the next customer will receive damaged glasses and you will have to face a buyer return for which you will be charged shipping and return commission by Amazon. Also there can be a negative feedback/review about the product and order.
Now suppose you shipped it through easy ship, you have the option to check the returned item by opening the package. If the product is damaged, you will not ship it again to a new customer and you will be saved from shipping cost and return commission. Also chances receiving the product in good condition increases many times.
in case of FBA you pay double shipping. One from your location to FBA warehuse and one from FBA warehouse to the customer’s location.
So it is better to get a printer and cartons and do the packing yourself. Or hire someone to help you.