Those are tests, not operations. They were against friendly targets, specifically consumer wifi/bluetooth devices (based on the wattages). Had the target been actively looking for attacks, the sub would have been located within seconds. You wouldn't do this against an attacker with any ability to respond physically. The only time this would be useful would be against an unsophisticated target, but then why bother with the sub?

An airborne drone could do, does, the same job at 0.01% of the cost and 1/0 less lives on the line. The sub is ridiculous overkill.