I tried those solid fuel ones while waterfouling when I was young. Sometimes it worked pretty good but was unreliable.

I have a couple zippo brand warmers that work great for a few hours at a time.

I don't use any of them consistently.

Bought my wife an Ororo vest, she has all bu quit using hand warmers.

“You never need fear a man, no matter what his size. When danger threatens, call on me, and I will equalize.”
Samuel Colt.

�Common sense is genius dressed up in work clothes.� - Ralph Waldo Emerson