Before you hand over your card, do a quick mental math. Think about how many puffs you take in a day. For an office commuter, that might be 20–30 puffs during the drive, and a few more in the evening. A 5,000-puff device could last you about two weeks if your usage is moderate. That's a decent benchmark.

Compare that to the price. If a 15,000-puff device costs twice as much as a 5,000-puff one, you might be getting a better deal—or you might be paying for a number you'll never reach. The choice is yours, but now you know how to read the label.