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Low fueling (charging) costs would be huge if they could scale it up to passenger size. It sounds like they probably can't, but even a hybrid jet/ion plane that use substantially less jet fuel could be a game-changer.

(Also, the fact that it can be outperformed by a sparrow is only relevant if we can build a reliable, efficient artificial sparrow, which AFAIK we absolutely can't.)

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This technology is inherently less efficient unfortunately, because the ion velocity is very high. The thrust-to-energy ratio goes to 0 as exhaust velocity increases:

mv/mv^2 ~ 1/v

You could lower ion energy by lowering the voltage, but then the thrust-to-weight is going to be prohibitively low (and at one point you won't be able to ionize air anymore?).

High efficiency flight means either wings or slow moving propellers (and aircraft itself preferably). You'd need to look no further than a glider to fullfil the potential claimed here. Overall flapping wings are probably superior though, since they allow vertical takeoff and high manueverability; but they're much harder to develop and maintain.

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