finding the ESR screen protector has quite a rough edge. With a case it wouldn't be an issue but without its a little annoying.
as for purchase options, UK 0% 24 months vs iup:
iphone 12 on iup - £56.45 per month x 20 months, with a £69 upfront charge. You can upgrade after 11 payments by handing the phone back. you can always choose to sell the phone and settle the finance which may save some money, but with the knowledge Apple will swap if you need to (in case resale prices fall a lot for some reason)
iphone 12 on 0% 24 months - £49.91 including applecare. No upfront. So £6.50 per month less expensive. If you want to upgrade after 12 months you'd need to settle again, and this time you'd have a higher settlement fee as you've paid half off, vs 11/20ths on iup.
I'm on 24monhts now - mainly because I could do it online and didn't need to go to a shop, which the iup required