I'm a Radion fan myself, which is why they are what I have on my tank (Gen4Pro like yours) , although I'll admit that some of that is form factor and I don't have much experience with the newer Kessils. To my eyes the Radion has:Better overall color renderingWorse light patterns on the sand bed (although this is correctable with the new diffusers at a slight PAR cost)The Kessil's have:Better shimmer on the sandbed (not halide quality shimmer, but close).A slightly blued out look (personal opinion here).I'm curious what specifically you like on one tank vs. the other, a lot can be done by playing with which channels are where. For example, I had white/red/green higher than most people on one of my tanks for a while. A lot of people commented on how amazing my clowns (basic ocellaris) and flame angel looked, asked me what I fed, etc. It took me a while to realize it was more lighting than anything else, of course my corals looked a bit different as I had much less blue.