No catch, volume is what they are after. I have returned thrice. Bought 7 times. They had a bug or still do that when you use a saved prescription and use that to order your glasses, the -ve cylindrical power comes up as +ve. I didnt notice that and ordered. sent it back in prepaid label and ordered another. Refunded my cost without any hassle. Next time my daughters temple arm broke 2 months after purchase. I sent them a picture, they asked me to send it back and they gave me store credit. They rock and this is very much inline with amazons policies.