Motorized blinds make managing light and privacy instant. You stop wrestling with cords and start controlling your room's mood with a tap, which is a major quality of life upgrade.
Installations usually take a few hours once the parts arrive. Wait for holiday sales at home improvement stores to snag the best discounts on the hardware itself, then book your installer during the off-season when they are hungry for work.
The 18-month window is a deadline, not free money. If you have a balance left when that time is up, the interest charges will kick in on the remaining amount, so prioritize clearing the debt before then.