When you buy, you own an asset. iPhone X models hold their value remarkably well. Once the phone is paid off, you can sell it on the secondary market to recoup a significant portion of your initial investment.
Buying the iPhone X—whether upfront or through a traditional installment plan that leads to ownership—is the pragmatic financial choice.
The biggest perk is the ability to trade in the phone for the newest model after 12 months. If you always want the current flagship, leasing ensures you aren't stuck with "old" tech.