Depends on what's "better".
They cost about 8 cents less each when bought in quantity but are too long to fit inside the padded flat rate mailer.
And it is an envelope...what made the box better for my purposes was that I was able to get all the protection of a box, the flexibility to ship 1 to 10 comics, while maintaining the ability to ship at an affordable flat rate. You can probably send that flat mailer by first class but, unless the buyer wants it sent that way, I never send comics first class.
Makes sense. Thanks. I guess you just have to use a lot more filler if you only have a few books.