I never used a warmer in mine, never felt I had to. I wear the strngfleece 220 under the glommit but it’s so when I take the glommit off my hands don’t start freezing immediately. IMO they are very warm and will be in my pack if it’s below freezing.
I’ve had a pair for 2 years now. They are good but not great. I tend to tick all my fingers in the main pocket. I think the Sitka Blizzard mitts are better. With that said I’m still rocking the KUIU.