Let me add that I used to do this - back in the "good ol' days when you could get 6 cookbooks for $1.00 :-( That was at least 22 years ago so they have been around for awhile. They are perfectly legit.
They will send you the featured (either 1 or 2 cookbooks, can't remember) if you don't get your card in saying you don't want them. BUT what you can do is call the company and tell them that you only want to order and not be automatically shipped if you don't get your card in on time. They will be glad to do that.
It's a great way to gain a great cookbook collection - that is how I got a lot of mine.
"Count yourself...you ain't so many" - quote from Buck's Daddy