Mittens are much warmer imo, and I think they look cooler as well. They are obviously less functional than gloves without the finger separation, but whatever. I'll take a nice pair of mittens over a nice pair of gloves any day.
It sounds like you've never actually used Kincos. For $12 I have been toasty and happy in sub-zero temps. There's a reason lifties, patrollers, and snowmakers all over the country use them.
The only problem I've had with Kincos is that they're really fucking stiff and I can't really hold my poles as well when I use them. They're warm but damn they are stiff.