I've tried it a couple of times. The last few I have made a styrophome wall inside the box. I think they work pretty well. One of the boxes I sent out was sent back to me with them refrozen. When I recieved it they were melted but still very cool and in crystal form not messy. As for cost. One did cost a couple bucks more, but the last one I made it into a smaller box, and cost was the usual $4.60 USPS Priority Mail
