I was on the twists for a long time, probably about 9 months. I probably had a few knockoffs but made sure my last few were genuine, which really didn't help with the issues.
Pros: Light, easy to carry in shirt pocket. Being able to dial-in the volts/amps whatever they are was a HUGE game-changer for me and changed my habit from sucking on a combination of Blu's and analogs to dropping the analogs completely.
Cons: Expensive, at $18 per battery, and always needing two in my stock at all times, I was finding myself replacing one at least every 30 days, sometimes more often than that. They broke a LOT. Not physically, but the electronics would go goofy, and it would do a number of odd things (each one had it's own demons), such as refuse to charge, crazy blinking patterns that nobody ever seemed to have seen before, connection to tank difficulties, impossible to read dials, twisters that were difficult to adjust, twisters that were so loose that they would just go min/max just from it being in my shirt pocket, etc..
I moved on to the Vamo, which I really do love, but after only 3 months, the center threads (using vivi nova 3.5 metal tanks) are all stripped out. I really hate the idea of going to kangar or evod simply because the unit can't support inside threads .. grrrrr. I've read here that it's a common problem. Ironically, I'm back on my last surviving ego twist from yester-year because of the annoyance of having to hold the damn tank onto the Vamo when I hit it.