I don't think it's too good to be true...It's just not a name brand. But I don't know. You can buy the same light directly from aquatraders.com for $20 less than what it is on Ebay.
I have a Coralife... I don't know if it's better or worse than anything else out there. All I know is it works.
Here's what I found out recently...you may want to find something with blue actinic bulbs in it 10k-14k. 14k will be more blue light than 10k. The MH bulbs are very good for growing corals, but they put off heat, some people don't like the added heat when they're trying to maintain a steady temp in the tank. And I think MH lights tend to use more electricity for some reason.
The T5 lights are very popular. You want to have about 4watts per gallon.