This is why I buy an android e-ink tablet.

My needs are unique, all of our needs are unique I suppose, but I want epub but also want to use the Kindle app (in cases of them being the only place to get a book).

I worry about firmware updates(security), but also my needs do not require the tablet being online constantly. So in a case like this, not a phone, not online, I only bring the wifi up to download books from Amazon via their Android app.

Otherwise, I copy epubs over via USB.

This is the middle ground.

I've been quite happy with the Meebook E-Reader M7.