What is the median use time amoung these devices?
I love the idea and on a different day might try to acquire one. But realistically it would end up in a drawer after not too long.
In ye olden days we had PDAs 'Personal Digital Assistants' some of which were in this kind of form factor, but then everything they did, addresses, phone numbers, notes, calculator is done by your phone now.
I also thought the same. It's a nice feature to have, but typing out significant code on that keyboard is a burden compared to a full-sized keyboard. Plus, it's not small enough to carry on the daily.
I personally believe the correct form factor for such devices is a smart watch, where code is written off-device and deployed to it, and the results of the code can be enjoyed throughout the day.
For example, I've developed(/ing) a Micropython based smart watch [1] where code is deployed onto the watch. The idea is to be able to deploy apps and interact with them via a simple interface. Being able to interact with my code daily helps keep the device relevant and to be able to make continual progress.