The Provari uses a more accurate technology to regulate the output power, so it is consistently and constantly the same voltage regardless of battery life. Chinese mods tend to operate around 30Mhz and the provari is up around 800Mhz iirc. Is this discernible in the hit? Some say that they absolutely notice the difference. I'm waiting on a CVI v1 so I can't really say myself until that shows up, but compared to a Twist there does seem to be
some difference.
http://www.e-cigarette-forum.com/forum/provari/381232-provari-oscope-vs-vamo.html
Of course it comes with a 1 year warranty and an optional 2 year. Only a few manufacturers offer a warranty that long and only one I know supersedes its (Super T's).
When they offer an upgraded circuit board you can send it for $20 and receive the update, instead of buying a new version of the device.
Their customer service is apparently really good but I've not had to contact them for anything.
It offers the lowest ohm capability of any VV mod that I know of. Mechanical is the only way to get lower.
They are bloody solid as a rock too. I've dropped my full size numerous times and the device, while marred up a bit, still functions exactly the same as it ever did. They feel real good in the hand, nothing about them feels cheap.
No experience with the Darwin. I think with all the VW coming out now its a bit outdated. Though its definitely a collectors item. Could look for something like the DNA20, same manufacturer but with better capabilities.
Keep an eye on the classified section. Provaris will pop up at very reasonable prices ($20~ under Provapes price). They also hold their resale value.