Like the person below commented, it’s a completely different beast compared to an iPad or an iPhone screen. It’s only intended to be a book so it might help to think about it like that - it’s designed to be as close as possible to paper, not a screen. It’s not a step down in technology, rather it’s a completely different tech for a completely different set of needs.

Put your ipad and kindle side by side in different conditions and try and read a page. In full sunlight you can’t see an ipad screen. In the dark an ipad screen is really really bright. In both cases the kindle lets you read easily. Because it uses e-ink, the screen isn’t made from glass, making it lighter and much less breakable. Because e-ink is only black and white it uses far far less power than an iPad screen so you don’t need to charge it remotely as often.

If you only read a few pages in bed before you go to sleep, you might not need a kindle. If the reflective screen and brightness of your iPad don’t bother you, you might just want to stick with that. But if you read a lot, read in the bath, or in the sun, or at night with the lights off, or if you have a physical disability that makes holding a book/iPad difficult - a kindle is the answer.