Title: These aren't going to protect anything from the USPS.
Review: These mailers are very thin and aren't going to keep sensitive material from being bent, or perhaps even folded. If you're mailing letters, then they'll work fine. If you're sending something collectible that needs to stay flat throughout the postal process, you'll be cutting a few up to use as inserts for the one you actually use to mail them. Keep that in mind when evaluating the price per mailer.
Is this product review negative?