From all the reviews and because these and the K5 1000s are sold out everywhere these are probably going to be excellent lights. But, I've seen the footprint comparisons. The Kind lights aren't square. Covering a 4 x 4 area with 4 evenly-spaced RW-150s is going to give you a very uniform footprint. It's very similar to the Apollo AT600, which is a highly regarded LED light, but at $2,449, it's a little out of my budget.
A Kind K5 XL1000 runs $1,695
4 a51 RW150s comes to $1,680 ($420 ea) if you pre-order them now. I think they make deals when buying multiple led lights so this price might remain the same.
I'm going to do a SCROG with 4 plants in a RDWC UC system and I'll post the pics of the grow. Can't start building for a few months though. Have to wait for a little money that's coming my way. It's giving me time to do lot's of research before I actually bought anything. I've asked some very important questions and got some really good answers from the community. I was originally all about the Kind K5 XL1000, but the more research I did convinced me that the area 51s are really good lights and have been out for a while. It's really proven itself as a really good LED light.
So, I didn't mean to speak badly about the Kind lights, it's just information I've picked up in researching all the different LEDs out there. This is nowhere close to the original plan I started with and my opinions are just based on the research I did.