Bar end mirror on drop bars? You should be fine.
I started using them this year. Previously I had a hard time keeping my hands warm. Now I don't. They're a fantastic product. You wear about 1-2 levels lower weight gloves. So, on a day when I might wear big ski mittens I'll just wear some thin fleece gloves. On a day where I might wear those fleece gloves I'll go bare handed.
One key to making them work well is to have something to keep the air from rushing into where you insert your hands. My solution is that my wind break is pretty baggy on my arms (jackets always are for me).
I have to use Shimano ones. I don't use the zipper to cool my hands much, I just pull my hand out for a little bit.