I am using the Xteink X4 as my primary e-reader now-a-days. Simple ESP32 microcontroller. Plastic+glass shell with an e-ink screen. MicroSD card works like a cache. Battery lasts for weeks. Works great.

Don't get me wrong. I like modern CPUs with huge caches and incredible power, but you do not need this for most devices. Also leads to lazy programming practices and calculators consuming hundreds of megabytes of RAM.