USPS Priority Mail Shoebox - New Item?

Is this a new item being offered by the USPS? If not, I've never noticed it before:



We stamp collectors well know how useful shoeboxes can be. I just noticed the USPS is now offering "shoebox" sized mailers for US Priority Mail and Express Mail packages -- at no cost. Regardless of how legal or illegal it may be, if these sort of boxes land on the post office counter as freebies, I can see many being put to use for other than Priority Mail parcels.