I never take AC+ for the phones as I get the new phone every year, so I basically put the AC+ money towards the new device, and look after these things inside cases – they don't always break, but just as importantly I don't want a phone with scratches all over it either, as it makes selling it at a decent price much harder.
(even putting the money in the bank as normal savings, and then if nothing goes wrong, you still have the cash, but anyway, other insurances most of us have already cover this better.)
But I *do* take plain AC on my £4K+ MBP, as I own them for minimum 3 years (normally 5), and so the £205 (from Ebay) for AC makes sense – 3 years of cover, and as if something like the motherboard goes on such machines it may cost £1500-2000 to fix, hence is actually worth it at only 5% of the machines value, compared to iPhone X which is nearly 18%!
The IUP seems stupid to me, as regardless of the apparent free AC, you hand the whole phone back to Apple and still owe them the rest; why do that?