The english version is one slot at a time, top left, the right, bottom left then right. As for them being independent, who knows but I don’t think that would be allowed? within one slot. I do know what you mean about the US types though where more than one different slow can be spun at the same time.
Anyhow, on this all four of them are linked via the 4REEL light up bonus. You spin the top left one, until the bottom right one giving a chance to add/light the letters. It resets after the bottom right one.
I prefer it to reel king simply because of that extra feature, the rest is the same except that feature can go crazy.