I don't recommend buying E8 or E9
E9 is KR808D-2, the incompatible rebrander model of KR808D-1. KR808D-1 is very popular - the most popular 2 piece - and there a lots of prefilled and blank cartomizers for it, they offer manual
batteries which are what most people here use and recommend, there is 3rd party support for KR808D-1 threading for new styles of cartomizers. KR808D-1 (Vapor4Life, SmokelessImage, Bloogplanet, Halocigs G6) is the smart
buy (and I recommend manuals) and E9 is not the smart buy. All that is available for E9 are auto
batteries, stuff from Greensmoke and Smoke 51 Duo and 2 kinds of blank cartos (Vaporkings has some KR808D-2 cartos and LeCig has some D2 cartos, and adapters for D2)
E8 is unsupported by anywhere except possibly some rebrander called Premium Electronic E-Cigarettes may have an E8 model.
So you can buy something compatible and take advantage of all of the stuff available for it, or you can buy E8 or E9