I sell my phone every 18 months. Technology is moving fast.
It's closer to break even (with AppleCare) than you might suspect; the variance will be on the policies around damage, wear, replacement, etc.
Also consider the out of pocket on taxes - my 128GB phone cost me around $1000 out the door here in Canada. (15%)
I think it's ~$20/mo depreciation over a 2 year period vs. $34/mo they're taking, but my time is worth something, and if they make it headache free - it's not as crazy as it might seem at first when you run the numbers. I'm already paying $120/mo all in for service - yay Canada.
Over 4 years? The depreciation is very high - it's stupid to keep the phone this long if you want a new one.
If things get so grim $14/mo is a problem, no, this service isn't for you - but it's not as crazy as you might first think. I'll probably take them up if the price differential isn't too crazy here over the US.