I have used them a lot and only had a problem once and that was when I did not fill the bag all the way. BTW, they are huge bags and add greatly to the total shipping weight.
My sister that has been a FW breeder for many many years has never had a loss with them.
I think Maria is right that sometimes you get a plane that doesn't have enough O2.
I have a ton of them if you want to pay the shipping I can send some to you. PM me if your interested. I got mine direct from Kordon.
But remember you need to really go thru the whole mess of getting certified by FedEx to ship fish. I know lots of people "get a away" with it, but why risk the lifes of the animals you are shipping? Why would you be risking them someone will ask... Because FedEx policy is that if a box leaks and the it not 100% (which is never the case) clear as what the leaking substance is, the box is deverted to the main hub for HAZMAT inspection/testing, which can add days to weeks to the transit time. They can also stop taking any shippments from you.
Also if you are going to ship in bulk, you would be a lot better off get an air freight contract setup. Air freight is the only way to go if you are shipping >75# at a time.
Also II... You can not ship outside the US without an import/export permit, which is easy to get. Just lots of little hoops to jump thru and HORIBLE instructions on how to jump thru them. It is amazing how three days of reading and research can be totally put aside by actually talking to a USFWS and US Customs agent for five minutes. :lol: