I think you've hit the nail on the head here. An e-ink tablet needs the same SoC, battery, metal case, and software engineering that an LCD tablet needs. So if an e-ink display cost the same as an LCD, the tablet would cost the same. But because of the limitations of the display technology, the device would do less than the equivalent tablet. You can't play games on it. You can't watch Netflix on it. Browsing the web would be a chore that nobody would do except in an emergency.

For that reason, the devices don't exist.

Something like a Kindle Paperwhite works, especially for people who read a lot of fiction. It's small, light, easy to read outside, and fairly cheap.But upsize it and now you have a very limited function tablet.

OK, it works for reading PDFs of things like scientific papers (which I understand is something people like the Remarkable tablet for). And it's easier to read outside. (Might be a bit cheaper too because you don't need as powerful a processor.) But you're mostly trading off a pretty general purpose device--which is getting even more so--for something that has a really narrow set of use cases. And isn't really as good as the smaller models for just reading text.

Not quite the same; battery needs are a fraction even with front lighting, CPU can be slower due to lower display refresh rate, displays are less fragile so you can have a less robust case, etc. Unfortunately, this doesn't overcome the higher display cost. Perhaps an e-ink feature phone would have a high enough volume to do so.

The Hisense A5 e-ink phone is available now for around $200and runs on Android 9. https://goodereader.com/blog/reviews/hisense-a5-e-ink-smartp...

I may have missed it but I can't see any mention of the battery life - surely that's one huge aspect.

I've been eyeing a Remarkable tablet for similar use. I'm an (avocational) organist and choral singer, and would love to have my entire library accessible at all times. The Remarkable has a smaller screen (10.3") than the PadMu (13"), but it is somewhat cheaper.

I made the plunge a few years ago to get a gvido device, which is similar. The big problem is the refresh rate on the device. It is incredibly slow to flip pages, which is a big problem when you're playing. I spent $1500, and the device is basically useless because it's so slow. And the japanese based company doesn't take open box returns, so now I'm stuck with it.

If the device could flip pages quickly, it would be an amazing device. It just can't.

I've ended up using an iPad Pro for this. It's a little more expensive but multi-function so I use it for more than music.