Yeah, that's a nice looking lamp, and a great price for a 3 year warranty!
You will need to deal with the heat from this light, tho. I thought that was why you had decided to use flouros, or maybe that was someone else.
Anyway, the 400w HPS will light a 3ft x 3ft area nicely, and will raise the temp in that area by 20-30 degrees. You will need to take care of that.