Just got my Keycool 84 2S in today.
RGB is all presets. For solid colors, your options are red, green, blue, yellow, purple (lavender), cyan, and white, and none (off). Everything else -as far as I can tell- is just some kind of typical rainbow effect. I am very happy with just being able to set it to white. There are 5 brightness levels, and the LEDs are as bright as the DREVO Gramr 84, and much brighter than its predecessor: the Keycool Hero 84.
The build quality is just as good as the original Keycool Hero 84, which makes it leagues better than the DREVO Gramr 84. Just like the original, the housing is solid plastic with a metal plate on the inside for weight. In contrast, the Gramr 84 chassis can be flexed in your hands and weighs less, though this shouldn't really affect normal operation...
The cable is detachable mini-usb, and comes with a transparent plastic bracket that can be inserted onto the plug body for security; it basically prevents damage from yanking on the cable.
I can't particularly tell the difference between the Gaterons and Cherry MX, so I see no problem. The included keycaps give it a hollow sound when bottoming out, but I will be replacing those with shine-through keycaps from Aliexpress.
I'm very happy with it, I think I'll buy another.
EDIT: Found out one more thing. The original Keycool Hero 84 and similar keyboards like the Noppoo Choc Mini had a numpad mapped as function keys under 789. It was a terrible numpad and we all hated it. Unfortunately, if you wanted to use a standalone numpad on the side, numlock on the external one would cause the functional numpad on the board to activate, so you couldn't use a standalone numpad with the Keycool Hero 84. The Keycool Hero 2S fixes this problem by completely removing the numpad feature. Thank. God.