Some one made a better version of my PocketBook koreader sync. Check ot out here
https://github.com/ckilb/koreader-po...sync/tree/main
I'm guessing that the koreader position doesn't exactly sync to pocketbooks native reader. I say this because of fonts size differences, margins etc
For the SDR issue. Read this it may help
https://github.com/koreader/koreader/issues/9265
I wouldn't be hesitant on using KoReader on android. It's completely safe. Just make sure to download from KoReader.rocks