Media Mail is a less expensive shipping option and the USPS now includes tracking with media mail, so at least if your product goes missing, it can often be located.
However, Media Mail does not include insurance against damage or loss--without insurance, we cannot replace your items if they are lost or damaged in shipment.
Additionally, Media Mail is less focused on timely delivery, which means that your products could be delivered later than you might expect, delaying your plans for using them.
CoVid-19 in 2020 Update: Several customers have told us that Media Mail shipments are taking three or four weeks, where they used to take a week or two at the most. USPS acknowledges the delays on its website, which also states that Priority Mail is unaffected by delays. Whichever shipment method you choose, use the tracking number to work with the Post Office if you are concerned about delivery or loss.