The tank and the firmware. The v2 kit comes with the tRon tank and 2.0 firmware (Ss support, new screen layout) pre-installed I believe.
If they don't say, then it''s probably v1 and you'll have to go to the joyetech site and upgrade to 1.3 or 2.0 yourself to get the SS tc support. 1.3 gives SS but keeps the old style screen layout if I recall correctly.