A smart mirror clears your view immediately after a hot shower and gives you better light for grooming. Once installed, it saves you from wiping down glass or squinting in shadows every single morning.
Wait for major holiday sales at home improvement stores to snag the best price on these units. Plan for a weekend project since you will need to handle both mounting and basic electrical wiring if you aren't comfortable with DIY.
Remember that the 0% period is a deadline, not a gift. If you have a remaining balance after the 18 months are up, you will start paying interest on what you still owe.