I think you've missed my point about using an interest free credit card as well. I could make identical payments to my credit card that i would be making towards the apple upgrade plan. Only a year down the line I can buy the 7S Plus AND sell my 7 Plus for several hundred to go towards it. Whereas with the Apple plan I have to give that phone back and take out the FULL credit amount for the new phone. Whereas with my way my second year credit amount would be the price of the 7S Plus, sub whatever I sold my 7 Plus for (£400-500 at least if I keep it in good condition).It depends on how much you get for your one year old phone. If you use the upgrade programme then you have a fixed payments. Just multiply the fixed payments and compare it to the depreciation of a new phone after one year
So this time next year I will only be needing credit to the amount of approx £400, instead of the full £819 using the apple program. (By selling my current 6S and with a bit of planning I can also easily clear the full amount by this time next year rather than needing 2 years credit which is also an advantage over apples two year program).