It's about reliability really. I am a fan of the Twists, bought my sister a couple about a month ago to get her started vaping. For what they are, they work fine. The things you get with a Provari that you don't get with a twist are pretty simple.
You get a non disposable device. This is a big one for me, but momma was a hippy, so I can see where it might not concern everyone as much. Sure, I dispose of batteries occasionally, but the core device doesn't go in the trash can like a twist does.
They are American made, and while I'm not against buying foreign goods, I do like to support our own economy if the price difference isn't insurmountable. Not only that, but it's not a matter of buying something of the same quality and spending a little more because it's American made, in this case it's a matter of the best quality available actually being American made. This also means you can easily mail it back to the manufacturer in the rare cases where something goes wrong with one, and they'll fix it for you even if the warranty is expired at a very decent price.
They are made of stainless steel, and I can personally attest that they hold up to multiple droppings in ways that I've seen kill lesser devices after just one. I've seen Egos fail from falling off a pretty low table, where as after dropping my Provari out of a shirt pocket while running across a cement parking lot I picked it up, wiped the dust off, and went back to vaping, it hurt the driveway more than my device.
So all of those are good reasons to buy a Provari in my mind, but they aren't even the real selling point. That's their rock solid reliability. Through a combination of quality design, quality components, superb manufacturing and excellent support, they just do what they are supposed to, day in and day out, over and over again. I just have to screw my vivi nova tank on, check the ohms of whatever coil I wrapped in it and set my voltage to match and I'm good for days. If the quality of my vape goes down, it means it's time to wrap a new coil for my tank. If it didn't shut down and flash a red light at me when I got low on battery power I wouldn't even know one was running down.
My experience with using a twist went more like screw on my tank after I make sure I'm using a coil that I know the ohms rating of so I won't blow it up, take a few vapes and twist the dial around until I find a setting that I can live with, and head out the door good to go, for a little while, then I notice it's no longer hitting right, and I adjust it upwards a little to find the sweet spot again, and then a few hours later I do it again, all day long until it dies, and at this point I had that dial twisted all the way over and still wasn't satisfied with the performance. It's not a bad cheap little disposable device, but that's also exactly what it is, a not bad cheap little disposable device.
No disrespect, but, I received my first real juices shipped to me today and I can not imagine a better vape than what I'm experiencing now with my $21.00 Ego T batt with a $3.00 22mm 2ohm cart and DK-555 from ECBlend born 8/12. I just ordered a 1000 C-Twist and I could have ordered 7 of them for the price of a provari. Just saying, they must really be something! 
I might own one in a few weeks depending on how much better the twist is. Like I said I can't imagine. 
