Each POD lasts close to as long as an entire original MONQ diffuser! If you buy a FlipCase, you get 3 pods with nearly 200 breaths each (600 breaths total).
Stored away from heat, and with end caps on, the pods should last over a year. If the end caps aren't used, there will be faster evaporation. If the pods are kept in the case without the caps, the evaporated contents will simply be released into the ambient surroundings when the case is opened.