Optic grow lights is currently the only company that offers cob panels. Area-51 is going to be releasing a modular COB panel in the next few months(don't quote me on the time frame). Plus there is the companies
@Greengenes707 started recently(pacific lighting concepts) and
@AquariusPanta (heavens bright) that will be utilizing cob panels. I'm starting a company as well for large scale legal growers in my state.
AS for why they're better, that would be raw efficiency. I think the blue chips used in bridgelux and cree cobs are around 80% efficient, and the phosphor coated in the LES does a great job of effeciently creating a very broad spectrum of light. This allows you to either get the same job done with less power, or get even more done with the same power displacement. Not to mention that cob based panels are simpler and cheaper to assemble than a comparable power level blurple panel.
You would get awesome results with one of optics panels. This one would fit you space very nicely.
http://opticgrowlights.com/120-watt-vero29-led-grow-light.html
The reason we always harp on DIY is because you can do it for a lot less money.