Depends on how well it's averaged. If you want to create a proper ex-ante insurance policy, you need underwriters, you need lawyers, you need adjusters, you need to determine premiums, collect premiums, pool the money, and then distribute it. These people all need to be paid, and so you must charge a premium over the actual cost.

Or, you can take the total lost cargo, divide it by the total value shipped, and send a QuickBooks invoice to everyone.

So long as the risk pool is large enough, and everyone involved is fairly trustworthy, it makes sense. Definitely unparalleled on land, to my knowledge!