When the photos drop, nobody looks at the drywall. They look at the color palette, the height, and whether the organic arch actually held its shape through the party. Getting a pro to handle that means booking about a month before the weekend so they can source your exact custom colors and lock in their install slot.
At a typical cost of $450, you are paying for their hours of blowing, clustering, and rigging the day of, plus the teardown. Since that hits your bank account all at once, you might want a way to space out the payments so you are not scrambling to cover it while buying diapers.
That 0% window is a deadline, not free money. If you still have a balance left when those 18 months are up, the standard interest rate kicks in on what you owe.