in essence, the IUP and 24 month Barclays loan are the same thing.. both offer 0% finance. The difference, as mentioned above by a few are the terms that come with each.
IUP
in my opinion, aimed at those who want to spread the cost of a new phone over a period of months, who want to upgrade yearly, and are happy to give the phone back to apple and start all over again the following year.
IUP involves:
- Apple Care is always added to the price (though you could just go and cancel it and get a refund for the remaining balance)
- initial £69 up front payment required
- total split over 20 payments
- you can only upgrade (hand phone back to apple and start again) after the 11th payment
as said above by
@mrandyyu, just handing the phone back to apple after 11 payments is not always the best value. In reality, the phone's value will be greater than your outstanding balance so you'd be better off selling the phone and paying off the balance and pocketing the difference. Also, with this, you can then cancel your AppleCare and get remaining balance refunded as well.
I'm sure there are plenty of apple consumers (clearly not us well-inclined folk

) who would just give the phone back and not worry about selling privately etc but to me its a little work for about ~£150 benefit.
This is what I did before Apple started offering the 24 month 0%.
24m 0%
straight forward finance agreement where you split the cost of the phone over 2 years.
- no initial payment
- no need to take AppleCare if you don't want it.
- no option to hand phone in with Apple and upgrade.
I moved to this deal when it became available a few years ago. Given I didn't ever just give my phone back to apple in the IUP, the benefits to me were:
- flexibility of taking AC+ if wanted
- spread over 24 months so slightly lower monthly payments (makes no difference as the balance at the end would be higher than on IUP)
- biggest win was the ability to pre-approve. Apple didn't offer at the time (and I don't know if they still do IUP pre-auth) the ability to pre-approve the finance days before the launch. This made the check-out process much smoother and not having to worry about cards blocked by banks etc (which happens to so many each year).
at the end of the day, the overall cost to you would be the same which ever method you took (they're both 0%) so its a question of convenience. To me, IUP is now redundant.