The eGo-c Twist is of course just a battery. You can vary the voltage from 3.2 to 4.8Volts. The regular eGo-c battery is a regulated batt that runs at around 3.3-3.4Volts underload. Both batts have the latest short and charge protection.
The advantages of the eGo Twist is that since you can vary the voltage, you really only need one standard atomizer/cartomizer/tank system rated at say.... 2.2Ω, and you can get wattages from 4.6 Watts to 10.4 Watts. That will allow you to find the right wattage for the flavors you're
vaping.
A downside to the eGo-c Twist may be the size and the length of charge - the 650mAh Twist is about the same size as a 1000mAh regular eGo-c batt. And the 1000mAh Twist is quite a bit longer than the eGo-c. The higher the voltage you use on the Twist, the sooner you'll have to charge. So even though it's rated at 650mAh (usually about 6 hours of
vaping), if you vape at 4.6-4.8 Volts, that time will be shortened considerably.... ymmv depending on your vaping habits...
The regular eGo-c vapes at @3.4 Volts, so those flavors that tend to get washed out or burnt at higher wattages, you'll need an atomizer/carto that is rated at above 2.4Ω. If you vape strong flavors as well, you'll need atomizers/cartos rated at say 1.5-1.8Ω to bring out the best flavor. IOW, you'll need a variety of attys/cartos of different ohms to get the most flavor at the fixed voltage.
The pros of the eGo-c would be that it is a smaller PV, you're going to get a longer time between charges - from 5 - 7 hours depending on your vaping habit - ymmv.... You're less likely to be burning out coils.
Both have the same 'eGo 510' connection and the best match is to get attys/tanks/cartos that have the 'ego skirt' that extends down past the batt connection - like with the vision stardust vs. the regular vision - otherwise there will be a gap at the batt connection. Same with smok tek's dual coils - you'll want the EMDCC made for the eGo.
If you go with the eGo-c tank system, I recommend starting with the regular resistance attys. And you should check these threads for the tips using the eGo-c. Some things right at first are important to stop leaks - prepunching the end caps of the tank, making sure everything is seated properly and other tips to maintain the system.
If you've always used cartos or cartridges with filler, you're going to experience a flavor explosion with the eGo-c tanks, vision stardust, CC cartos, vivi novas, etc.
I beta tested the eGo-c system. That was in December. I'm basically using the same components I had then and have added to them. I've lost three atty heads since then - two were LR's, one standard. I only clean the heads when the draw becomes tight. And I can go for weeks and sometimes months without having to do that. I split up my vaping by flavors and I have a few flavors going - about 6 or 7 and a pv for each so I don't really power vape one PV unless I'm testing something out. Splitting up your vaping like that really helps reduce problems

You might not be able to do that all at once - I didn't - but you can build up to where you can and it is factor on longevity and problem free vaping, imo. So at first you might keep a few of your V2 cigs going for that reason.... then add another eGo when you can.