Just wondering if you opened up a ticket with Jantyusa and see what the problem was with the carts?
Where did you buy the kit? did you go back where you bought it and let them know about the carts?
I have an eGo too and in MHO, it works very well. The carts I got with mine fit the atty's well and the warranty is better than a lot of others out there. 6 Months for the entire kit, nothing to get upset about.
Please, go back to where you got the kit and let them know about the carts being wrong. Also do try one of the other atty's and carts for the 510 you have. The cone is to keep the heat in and allow the liquid to be warmer than normal. As for the cart melting, did you line it up with th atty?
Go to the Janty sub forum here on ECF and open a thread and let Ethan or Mik know. Might be the wrong carts being shipped with-in the kit and they would really like to know if thats the case here.
Best of luck in which ever way you decide to go.