Honestly, 0% financing is better financially anyway. I buy outright for peace of mind, but really if you can pay monthly you can do other things with the money you would have spend up front.
Apple makes an incredible processor for its phones. That just makes them so futureproof down the line. Plus, you get 4-5 years of software updates. That's just amazing.
I think this is the main beauty in iOS, other than more consistency in design and support, is he Security Patch and OS update support.
I realized that the iPhone 6 Plus will still be getting iOS 12.4 at some point in the next few weeks along with other devices that came after it, compare this to devices like the Samsung Galaxy Note 4 or Google Nexus 6, both of which were iPhone 6 Plus competitors in 2014, both have not had an OS update in about 2 years now.