Yes, it is different - the others you mentioned are 3-piece - battery, atomizer, cartridge. The KR808D-1 is a 2-piece - battery and cartomizer - the atomizer and cartridge are 1 piece. The cartomizer holds a good amount of fluid (about 1ml) and lasts quite a while (I typically use 2-2.5 cartomizers per day). In contrast, I have a 901 setup also and have to top it off with juice after just a few vapes. The cartomizers are designed to be disposable, but are refillable, anywhere from a few times to over 20. See the stickied threads in the Vapor4Life forum for tips on refilling the cartomizers.
The Chuck is a battery mod (a very nice one, from what I can tell) - it essentially is a bigger device that gives long battery life. The 510's weak point appears to be poor battery life, from what I understand. Battery mods such as the Chuck solve that problem. Some other battery mods also allow higher voltage to be used (5 or 6, vs. 3.7). The Vapor4Life pass-thru also operates at 5 volts, where the batteries run at 3.7.