I don't think they're that overkill. $125 for a 36"-48" fixture is downright cheap, and that fixture uses 1w LEDs instead of the 3w everyone uses for DIY/the highend fixtures use, so it's not that bright of fixture. Comparable to unreflected T5s IMO.
If you want that fixture for the moonlight, you will be disappointed. The light only has a switch that either runs the blue leds, the white LEDs, or both. There is not a separate plug so you can run them on separate timers. You would have to manually turn the switch to blue LEDS, then back to both during the day.
The second issue is color. Those fixtures use bright 1w LEDs for the white light, Which IIRC is around 8800k. The blues are standard Radioshack LEDs, so they can't provide the same 'blue' you're used to with actinic bulbs in other fixtures. From what I've seen, they give the tank a slightly freshwater appearance.