Why does this actually matter?
Because the wrong tin means an addiction warning printed on the lid, a crash by 2pm, or both, and a habit you did not really choose.
Getting through a long workday should not cost you the hour after it, and it should not take a fistful of supplements and a fourth coffee. If the same half hour also carries an oral care ingredient, that's worth having. If it doesn't fit your day, you won't keep it.
Rule #1: Read the panel for nicotine first. Plenty of tins sold as energy still carry it, and the front of the tin will not say so. The ingredient panel is the only place that will.
Rule #2: Ask what it charges you in the hour after. Caffeine on its own is a jolt and then a crash. Look for real L-Theanine and Alpha GPC beside it, so the lift comes on smooth and comes down the same way.
Rule #3: Look for the complete stack. Nano-hydroxyapatite supports remineralization of early demineralized enamel, and xylitol supports a cleaner oral environment. Most tins list nothing at all for the mouth.
Rule #4: Check that the brand prints a ceiling. Two an hour, four a day, in writing on the tin. If a label never names a limit, you are the one guessing at 4pm.
Rule #5: Buy from the official shop. Steer clear of random marketplace listings and tins you can't verify, and don't write off a whole category because one brand was light on caffeine.