I think GreenGenes point on the cost is right on. They are, in comparison to 3w/5w diodes, more expensive. If you look around on Aliexpress, there are many COB-based LED fixtures, but of course not using the highest quality components, they're just pumping them out like they tend to do with many things, in volume, quality/efficiency is just an afterthought to most of the chinese volume manufacturers. From what I've seen on there the focus (COB) market right now for some of them seems to be the commercial lighting area, tons of spot light fixtures, outdoor lighting, high-bay fixtures, using COB's, but who knows what they're using for parts and how reliable/efficient they would be. I know from pricing out my DIY stuff using the Cree 3070's, I could buy a higher end panel like an A51 by the time I'm finished. But I'm a sucker for punishment and like the the thought of DIY, even at the same price. Spec-wise they should be more efficient though, we'll see. Of course a commercial panel builder could reduce those costs compared to one-of DIY projects, but, they would be expensive panels right now imo. Would they charge $995 for a Cree 3070 COB 200W Panel from A51? idk what they'd charge if they were to build them right now, but I'm pretty sure they'd be a lot more than $495...