You asked about the difference between the OR IT2040 and the Kessil unit. Well, I have little experience with the Kessil. but I had a
$750 Eco Tech Radion led fixture over my 24g frag tank. I tried an OR D120 (made by EverGrow) and it worked just as well for growing my coral, but I gave up the sunrise and sunset control. I didn't care since this was just a frag tank.
Oh, and I saved $600, can I say the Radion is kind of pricey! Then I tried the OR Arctic S026 and I like it even better than the D120. Better light spread, cooler running temp (like room temperature cool), less 'glare' at the light source and just look at it, it's a better looking fixture (slimmer and more modern looking).
If you want sunrise and sunset control (and I wouldn't be without it for my display tanks), look at the OR IT2060. I have 2 of the OR IT2080's over my 180g tank and an OR IT2040 over my 70g hexagon anemone tank. The IT series are well made, produce more than enough light to grow anything and cost less than most other fixtures. My OR IT series lights have been running 24/7 (because they have moonlights too) for 9 months and they haven't missed a beat once. They even hold their programming after a power failure. And being in SW Florida with all our thunderstorms, we know power failures! Even after a 10 hour outage everything came back on perfectly!
Here is OR's sponsor forum here on R2R:
Ocean Revive LED
And here is their website:
OCEANREVIVE LED
Here you can see the 2 OR IT2080's over my 180g tank.