It is slightly more expensive to start with but in the long run it evens out, you refill your carts just as the 3pc crowd or KR808D-1 crowd can, in fact it's easier and no mess with the GC, just get a needle and inject it in from the metal end of the cart that attaches to the battery. Simple and fast, no mess you don't even get liquid on your hands. The old adage is very true in this case, you get what you pay for. If you want to spend your time topping off, refilling the cart, or modding it so it works better than by all means get a 510, if you want your cart to last you a full day at work and then some you spend the $10-$15 difference and get the GreenCig kit. It's really worth it I have to say. I wish I had gone there at the beginning but I just didn't believe the claims about the cart life, now I know that it is true. Considering the atomizers get replaced about once a month or so then it all evens out in the long run with the cost.