Well, I have owned both. I think both are excellent lights and only have slight differences. The radion XR15 pros I owned put out more par than my kessils A360WE, but part of that was due to the fact that I ran my kessils on a very blue setting so I was not utilizing the white LEDs as much as I was on the radions. Also, the kessil wide angle lens gives a slightly wider spread than the radions. I mount my lights very high above the tank (like 16"), so the kessils give me very uniform par but lower par numbers versus if I used a more traditional mounting height. Overall, though, I still believe the radions were probably more powerful but I can't say how they would stack up against the newer kessil. As far as even spread, color separation, and shimmer, the kessils were definitely superior. I wouldn't be concerned about hot spots with the XR15 pros like I might with the XR30s that has two pucks closer together. In fact, I think the slightly less wide angle lens on the radion would be helpful for the 24" tank depth. The color separation on the radions, though, is noticeable to me but not that noticeable when ran with T5s (or if diffusers are used). The shimmer on the kessil is great. With T5s being ran, shimmer from either unit is going to be muted down, though, and probably not a differentiating factor. Ran by themselves, kessil shimmer is better than the radions. As far as controlability, I think it depends on what you prefer. The simplicity of the kessil controls is appealing to me personally, but if you really like to fine tune things, the radions would be better suited. Of course, this may not be true when comparing to the new kessils, as I'm comparing the radion XR15 pro to the older kessil A360We model. As far as color, I think both lights put out nice color. Kessil makes their own LEDs but I believe they are quality. The radion LEDs are quality chips from known high end companies (such as CREE Royal Blue 450 nm).
