If they make sense for you, then use them! I wasn't telling you do do otherwise.
But I have to disagree with the point that Samy's processing and shipping takes costs up to the $10.50 cost per roll that you named for using the mailers. And of course you would be mailing in batches at a time. It would not make sense otherwise.
...and yes, I have used mailers. In fact, I asked twice in this thread where to get them, because, as you said, they may be useful in certain situations.