I ship about 100 pieces of coral per week through USPS Overnight. So on average I sent 10-15 boxes of coral through USPS Overnight per week. What they meant by covering the package is if the package is guaranteed to be delivered by noon and it gets delivered at one then they will refund your shipping cost. As for insurance on live coral and live fish they will not cover it. It does not matter if the box gets crushed, its not covered. The local PostMaster showed me the stipulations for live fish and it basically states in no way or no how will insurance cover a dead loss.
I have shipped thousands of boxes of coral over the last couple of years through USPS and I have found there service to be great. The buyers really like it because it saves them a ton of money on shipping.
What most people do not know is that USPS does not have overnight air service planes. So, your USPS package either gets shipped with UPS packages or FedEx packages on there planes. This is what I have been told by two seperate PostMasters.....
I have also used UPS and FedEx, I always leave the option open to the buyer. Out of USPS, UPS and FedEx they have all lost a package or two that I have sent. But, I use breathable shipping bags so even if the coral are in the box for a couple of days they still arrive healthy.