A good mesh system should last you at least five years before it starts feeling slow. Buying a reliable setup now means you won't have to deal with dead zones or upgrading again when the next standard rolls out.
Check the release cycles for major brands. When a new version hits the shelf, last year's model usually drops in price while still performing perfectly for most homes.
The 0% intro APR is a deadline, not a gift. If you still have a balance after 15 months, the lender will charge you interest on the remaining amount, which will cost you more than the original price.