So is the GGR Rebel brighter and more evenly lit than a similarly set up 10W LED?
much brighter yes especially when you consider the voltage and current used but there is a little flair at the bottom. I like it that way though and am not a huge fan of the perfectly even blade everyone always asks for. That being said its not that much of a flair.
I have a video somewhere that compares the GGR rebel, GGW cree and RGGB LEDengin. The cree I believe I had in series running off of 1A (7.4V). The RGGB was parallel at 2A (7.4V) and the GGR rebel was running in parallel on 3.7V direct drive (off of CS). The current I was getting when I checked it with the meter was about 1.4A (so 700mA each dice).
The Rebel was the lowest voltage and least current and was brighter than the other two (just slightly brighter than the cree) but both the cree and rebel pretty much just washed the RGGB out. I have been told though that some of the RGGBs just didn't have very bright G dice though so maybe that was an issue. I have not compared it to a GGGG.