The only thing they changed afaik - they returned the first version of Neo Reader alongside with Neo Reader 2 to get back the ability to open files with Adobe DRM copy protection. So there's no point in updating if you don't use this feature.
Updates are quite safe. Actually I don't remember a single issue reported. The only exception is having something unexpected in new firmware version: like new bugs in every second release or the absence of google apps in one of the updates for the Chinese users in the past. In case of such misfortunes you can always just install the previous update.zip. However I don't remember if there's a firmware version lower than 1.8.2 for C67ML Carta2+
You can make a full backup of the firmware and software with rkDumper to have a dump to restore with the help of rkAndroidTool in case of running into troubles. You can find rkDumper here
https://www.mobileread.com/forums/sh...d.php?t=288387 and rkAndroidTool somewhere on this forum too.