I use and love chopper miits with wool liner mittens. Good to -5F (-20C) when I was young and probably +5F (-15C) now at 70. Deerskin leather. Used for chopping wood. The trick is to buy the largest size possible. I have narrow hands and long fingers. I get XXL anytime I can.
I treat them about once a year with Snowseal, a beeswax dressing. I love that they do not slip on the handlebars. While I lose some summertime hand positions due to the "webbing" of the mitten, in return I gain some because of that non[slip tendency, allowing positions that would be dangerous or tiring in summer. Also love that they are so easy on, easy off. Pulling one off mid-ride to reach into a pocket to get a snack then putting it back on while riding doesn't take skill.
Another plus, as it warms up, just pull out the inner mitts. Leather shell only is good to 70F. And easy to dry when you get home.
Lastly, a question about BarMitts - can you use both the drops and the brake hoods while riding or are you limited to just one (and do you get to choose which)?