Craig,
I don't the ones i've had have caffeine in them. Though, i'm not 100% certain i'm pretty sure they don't. I'm not sure if it would make a difference to me anyways because i drink a lot of coffee, redbull etc.
I think if i was going to do serious endurance events where i'd be on the move for hours at a time and, most likely, dehydrated i think the caffeine would give me headaches.
It would be different if i was using it in moderation for a short say 5k race distance but for hours under a ruck or on the road i'd personally stay away from it. Then again, everyones tolerance is different so maybe give it a shot and if you get headaches then you know its not for you, right?
Theres other metabolizers, aside from caffeine, if your looking to increase your heart rate and core temp for wieght loss purposes that are more effective, don't give you the jitters and headaches. I'm not sure if thats what you were looking for but it's out there-as you probably know..
Lastly, Its a great feeling when you wake up and you've got loads of enegry for those pre-breakfast runs, eh? I know how you feel and it's a great excuse to eat big suppers!
Bear