As with most insurance, it's not a positive investment in aggregate, but it is if you're the subset who needs it.
iPhone 7 at AT&T looks to have a $225 deductible. Screen-only is $49 (who repairs it is unknown) - it's $125 through Apple directly.
A used iPhone 7 128GB is about $385 in Good condition through Swappa, which I've used before.
At $9/month, and with used phone prices falling over time, that's about 15 months of insurance costs to equal the cost of full replacement or 8 months for screen replacement.
You need to decide on how long you think it would be until replacement is needed, and the value of cost certainty vs. a one-time larger cost at an unknown time.
AT&T still has "contracts"?