As cool as this is, why not humans doing similar work?
A 10 or 20 million dollar vessel and cargo is clearly worth a few hundred grand extra for external escorts. Just build it into the shipping pricing model.
Banks do that even when they carry far less. So two armed guards are ok to service an ATM, but no armed guards for a large ship in troubled waters?
One popular answer is that ports and countries don't allow armed vessels. My answer to that is, if authorities in Dar Es Salaam or Mombasa don't allow armed ships, don't send any ships there. Let Mombasans eat cake, or whatever they have, until they understand the realities and come up with a reasonable solution.