All I am doing here is simply offering my experience with this deal:
A while back some other eyewear company had their same deal - free sunglasses, just pay shipping. I bought through them (forget the name), and was satisfied. Got a decent pair of sunglasses for about $15.
Then this winter I jumped into my car, after de-icing it and sat right on them, breaking them.
Now I see this deal in Maxim/FHM or whatever and see it as an opportunity to replace them. I go online and purchase a pair. My credit card is charged $13 as expected, and they came in the mail a few days later. Sweet I thought.
I am very happy with the sunglasses, HOWEVER. I look at my Credit Card history and ANOTHER charge of $19.90 had been charged to my credit card, on top of the original $13. WTF. So I call their support line and it's busy, day after day. "I just got scammed" I thought. Finally I get through about a week later. The lady (rather rude, from dealing with angered callers such as myself all week) informed me that I did not purchase a pair of sunglasses, but a SUBSCRIPTION to 2 pairs every month. I said NO, I did not do this, it said nowhere on the site about it. She said it does say on the site. I retorted that it did not and she said she cancelled the subscription, and since the 2 new pairs had already been shipped, I just have to wait to receive them, write "return to sender" on the box and give them back to the mailman for my refund. So now I am waiting to do that.
Out of curiosity, I went through their online ordering form again in search of notice of this subscription and did not see anything about it.
So that is MY experience, hopefully yours are different, but PLEASE check your billing history!