Having both the Prime HD on my nano and 3 kessil a160 on my 80, I lean toward the kessil. Yes the prime has a lot of control features but you can't beat the look of a kessil in the water. The prime has noticeable color banding "disco" effect. I am probably more sensitive to the disco since I see both lights daily. For the price though, the prime HD is hard to beat. I'd keep an eye on the for sale section here, especially with the 360x coming out I'd bet you will be able to find a good deal on the kessil lights and controller.
I agree that the Prime has more features, but I also believe that there is beauty in simplicity and kessil has that spot on. Can you comment on the noise level of the Prime vs. the Kessil? And yes, kessils are a bit pricey new so hoping there will be some discount coming around this month or keep an eye out for lightly used ones.