They're expensive. ~300 USD, while the e-ink and design is nice that's a pretty big bill for something that does less than a modern phone that is also cheaper.

Previous discussion (2020): https://news.ycombinator.com/item?id=21943649

I think the most cost effective solution is probably buying the cheapest used A12+ iPhone one could find. Factory restore, then setup Assistive Access or parental controls, which can limit any ability to install apps or settings without a different passcode to unlock the phone. Have a friend or partner set that passcode so you can't be tempted to add anything smart to your Dumb Phone.