Just FYI, those I believe use the 5mm leds which are much cheaper to buy but do not have the same Watt/Lumen ratio as the Cree or other 3-5 watt lights.
I'm not saying its a bad deal, but to get the equivalent lighting from those as the 3-5 watt lights it's not going to happen.
I have built a panel similar to that and it works well and delivers light at the right wavelength for photosysnthesis, but I would suggest suplementing that with a t5 fixture as well.
Just my 2 cents.
EDIT: if anyone wants to see them I can post pictures. I think I paid aroun 60 bucks to build it, i can dig out the reciept if you would like.
EDIT 2: WOW 34 bucks, I paid too much to build my own! For that price forget everything I said!