There aren't many devices that are both low power and require a steady 1.5V operating voltage. Most will tolerate 0.8-1.2V as their low end. In a high drain device, the number of watts left in the cell when the voltage drops below that low end is minuscule, so this sleeve will only buy you a few more minutes of use. In a low drain device, it can give you a significant amount of time but most low-drain devices that would benefit already have a similar circuit built-in. Logitech's wireless mice and keyboards that use alkalines and last months, for example, have this voltage boosting circuitry already, and tuned to the minimum voltage the mouse requires to reduce conversion loss.