One cup of coffee has ~ the same if not more caffeine than one piece of gum.

Drip 115-175
Espresso 100mg of caffeine 1 serving (1.5-2oz)
Brewed 80-135

The regular coffee drinker who drinks 3-5 cups every morning most likely wont even notice the affects of chewing 1 piece of gum.

I also wonder how much of the 100mg in the gum is actually used/absorbed by you and how much stays in the gum.

Probably a waste of money unless you chew all five pieces at once I would imagine?