[Brett66]

16 months to the moon, man, this isn't the most powerful propulsion system. I guess ion drive is still useful in reducing the tonnage of such a probe.

[RightWhale]

The ion motor could barely move a feather. Of course it adds up after the passage of time and eventually the ship goes a lot faster, but eventually there is also a tradeoff. This would be impractical for manned flights: supplies for 16 months compared to supplies for 10 days, big difference. Even for totally automated ships, though, 16 months begins to bring in factors of expected lifetime and failure rate of electronics that wouldn't be significant for a 3-day direct flight. This is their first flight test, so we'll call it an experimental craft and consider mission success as a bonus. It isn't the first ion motor in space, but it could set a kind of record: slowest ascent to the moon. Maybe a solar sail could do it slower, there's a worthy goal.