I have the Vapor King. In it's onset, yes, it was pretty much the KR808. However since then, improvements have been made to the vapor king in pretty much all categories, vapor, throat hit, flavor etc. As it stands today, the vapor king and KR808 models do have compatible parts (use the carts with battery and vice -versa) however, they are really not the same anymore. In my previous KR808 models, I've noticed that the carts burn very fast. When you take them apart, there is nothing but burnt filler inside. With the vapor king carts, you can now go up to 2-3 refillls before they start to burn off and need to be disposed of. The batteries also have 4 holes as opposed to 2.
I have had many different models and juices since I started vaping back in October. My Vapor King is my primary e-cig. All my others are just sitting in boxes as back-ups.