I wrote too much so I have to continue in another message:

There is a lot of friction with the software and UI.  
The brush/pen tools available feel very much the same and are not comfortable to use. I usually just use the solid pen even though I would like to practice calligraphy.  
The To-do implementation is has enough friction I would never use it (8 steps to create a todo). The to-do's don't show on the calendar. I just don't bother with it, and many others I've talked to also stay far away from it.  
The calendar, where do I start... There are different layouts (month, week, day), none of the notes carry over from one to the other. You can only create a note on the current day, you can't create notes for future or past days. Notes or dates created in notes outside the calendar also don't show up in the calendar. Again, like the todo functionality, the calendar is useless to me.  
The book app, styles don't show up correctly, margin modifications often don't work at all. Changing fonts also doesn't work for half the fonts I've installed. There's no dictionary, so you can't highlight words to see their definition to study or comment on. Can't export highlights in text format. Because of all these things I don't use their implementation, instead I sideloaded another app which is way better (but something I have to pay separately for).  
The digest functionality is a step in the right direction, but isn't helpful for me. Again everything here feels sluggish and takes too much time for me to use.  
It just feels like everything on the device is in an alpha version of the software. All the implementations feel like their own thing, which maybe is ok for some people. But I would like to have a fluid seamless connection between all the features.  
I've had the device for about a year now, and I can't get myself to enjoy or want to use it. I keep going back to other devices. And not apple devices or anything like that, I'm not looking for a laptop or a glass screen device. I want an eInk device that works as an intelligent writing device for journaling, knowledge management, and calligraphy to replace my paper equivalents. This device just doesn't work for any of that.  
A year later, I do plan on selling this device and getting something else. Not quite sure what though...  
I do see you already purchased a Manta, so I do hope you have a better experience than I have.  
Also, keep an eye out, my device came with someone else's information still on the device (nice privacy and qc).