I agree with Kurt here, but just wanted to add something. The eGo Twists are significantly longer than a standard eGo battery. In comparison, I own a 650mAh Twist, and it's the same length as my 1100mAh eGo-T battery was. My Twist is 3 7/8 inches long, my 650mAh eGo-T battery is 2 7/8 inches long.
Also, the non-twist-eGo models are regulated to 3.2v. If you wanted something a bit more solid/flashy than the Twist, you could look into a standard 3.7v mod. There are tons of them around, but they carry a bit higher pricetag. Typically (not always) when you see the term 'mod' it's referring to something that holds a battery, has a button/switch, and a connector. Batteries on them are replacable, and typically fairly affordable.
Then they come in two flavors: Fixed voltage, and Variable Voltage (And Variable Wattage, but that's fairly new). Fixed voltage means that if you buy a 3.7v device, you're vaping at 3.7v with that device, and there's not an easy way to change that. Variable Voltage lets you play with the power that you're outputting. Typically you'll find fixed voltage is 3.7v, 5v, and 6v. (There are other configurations to get different set voltages) Changing them generally requires changing types of batteries and using different types of batteries in your mod. Variable Voltage uses a booster circuit to change the voltage when you turn a dial, press a button, twist a knob, it's fairly easy to handle.
Though again: I do think that the Twist is an excellent device for stepping up from a standard eGo, it gives you a new knob to play with without overwhelming you with extra things. Your old eGo charger will even work on it.