The BreathiZen bottle is 60 mL (2 oz), and general airline rules for liquids in carry-on bags use a limit of 100 mL per container.
On volume alone, 60 mL is under the common 100 mL limit, but rules vary by country and can change, so check your airline and airport before flying. This is general knowledge, not specific to the product.
Pack the bottle in a clear bag with other liquids, keep it in its original packaging so the label is visible, and bring a spare for a long trip.