The missing integration point is reading progress. The killer feature (for me) of Kindle is that I can have several devices and continue reading on any of them

The missing integration point is reading progress. The killer feature (for me) of Kindle is that I can have several devices and continue reading on any of them with my position in the book synced. I want that across different readers. For example, if I buy now Xtelink X4 for reading ‘on the go’, there is no easy way to switch back to a larger device for more comfortable reading at home.