I'll answer only what seems essential to me:
The operating system cannot be exchanged on any device - Boox uses Android 10, Likebook Android 8.1, I do not know the others.
None of the devices make calls to China.
The 10.3 inch devices have the same pixel count as the 7.8 (1872×1404) - Likebook P10 (10 inch) has less (1600x1200).
I go for 10.3 only when I use the device further away from the eye.
Mainly I use 7.8 inch devices - at appropriate (7.8/10.3) distance there is no difference.
My favorite - when I don't need a pen - is the successor of the Likebook Mars, the
Likebook P78.
Likebook has an important advantage for me - SD card capability; no other brand can do that.
Regarding speed of Boox or Likebook, I have not measured anything - it is sufficient for me.
And as a browser, I would generally use the system's internal one - it is tuned to the hardware.
Edit: The Boox devices have 2.4 and 5 GHz WiFi; Likebook only 2.4 GHz.