The fact they don't give any hard numbers is a pretty big sign that this is nothing more than a neat toy. Powering LEDs takes very little energy - 1 mA at 2V (2 mW) is enough to make it visible. Making it flash reduces that power again.

The concept of using bacterial spores as a means of producing motion is pretty neat, though it's obviously a long way from being practical. The suggested use case (low power remote floating sensors) seems pretty suitable for solar power, which has the advantage of maturity and no moving parts.