Because the phone itself is still fine and works really well, just the battery doesn’t hold a full charge and doesn’t deliver the full output current anymore.

Because the phone itself is still fine and works really well, just the battery doesn’t hold a full charge and doesn’t deliver the full output current anymore. Now I can use the phone for another 1-2 years which is great. I love the form factor as well and right now Apple doesn’t have anything comparable, but I hope they’ll make a small phone again. Also, the unofficial replacement is not that much cheaper, you get a no-name Chinese battery (which is often worse than the original and more dangerous) and it might break things like FaceID/TouchID because the security chip will be reset and the non-official repair shops don’t have any means to reprogram it (as far as I know).