Which CrossInk firmware to install?

I just got my X3 locked unit last night and tried the stock firmware for a bit. I wanted to use it for at least a couple of weeks, but it's hard to use. I like the app connection tho but not for reading. So I tried flashing to Crosspoint via SD card as a tryout, and it works. Now I want to flash CrossInk, but there are 3 .bin files in the releases.

firmware-teensy-v1.3.4.bin
firmware-tiny-v1.3.4.bin
firmware-xlarge-v1.3.4.bin

What's the difference, and which one to install?
And my epubs are not showing book covers, both in stock firmware and in Crosspoint. How to fix it?

Thank you in advance 🙏🏻