This method is intrinsically cheaper than delivery by automobiles. I expect it to catch on.
I doubt this method will work when winds are gusty and high.
Also subject to problems not faced by delivery drivers. Birds of prey notoriously don't like drones and attack them. Now the birds can get food by attacking drones. The weather, of course, is also an issue. At least the 300ft altitude will make thievery more difficult.
Be interesting to see how technophilic theory compares to reality.