Did the charcoal sticks for years and they were steadier but cases would wear out and messy to clean. Finally settled on the disposable heat packs which were very dependable and handled roughness and compact and flexible in mitts
I tried the Zippos's years ago but didn't like the smell or the irritation they caused on my skin when in my pocket. I switched to the charcoal sticks and liked them much better but had the same issues as you. I then switched to the disposables and still use them.
One issue to be aware of with the disposable hand and foot warmers; they have a shelf life. I had some at camp that were years old. I took them with deer hunting one morning and about mid-morning when I started to get cold I tried to use them but they never got warm.