I've just started paying monthly for Apple Care+ in the UK for the watch. Comes to £4.49 per month and just keeps rolling until I cancel it. By the time I've made 20x payments, I will have reached the £89 for 2 years.
I tend to only keep my watches for 12-18 months, so this works out to be more convenient for me as I don't need to seek out the refund and handover £89 after just having handed over £649 for the stainless steel watch.