Is there an actually quality difference between the ego-c, e, t, etc?
Yes. In the Joye line ...
eGo-t upgrade, eGo-c, eGo-c upgrade have the 5 click on/off feature and the 'charge indicator' on the led button from white to dark blue.
eGo-t upgrade has better short and charge protection than earlier eGos.
eGo-c and eGo-c upgrade have even better - best in style - short and charge protection.
eGo-c upgrade batt has two modes - regulated at 3.3-3.4V and unregulated 3.7V mode where off the charger you're
vaping at 4.2V and then to 3.7V for most of the charge, falling off to 3.2 at the end. It isn't 'full VV' like the Twist but it does offer a bit more voltage in the unregulated mode.