You want a headset that cuts out room noise and lasts for years, so you only buy once instead of replacing a flimsy pair next year. November is the right time to shop because holiday bundles usually throw in extra cables or charging stands for the same price.
Check the release cycle before you click buy. When brands drop a new version in the fall, last year's model gets marked down even though the actual sound quality and mic performance are nearly identical.
Remember that the 18-month window is a hard deadline, not free money. If you still carry a balance when it ends, interest kicks in on the original amount from day one.