That's completely up to your decision.
Do you
really need the new features in 5.8.9? (Speaking for me, as I'm only using my Kindle as a good hardware base for reading only offline, public domain, classics primarily either in epub/mobi or PDF format, I'm not interested in "special features" for Kindle native formats and/or Manga books, so 5.8.7 is more than sufficient for me.)
If you really need the "new features" and can guarantee to stay always(!) in airplane mode (to avoid unwanted OTA updates, which could break the jb in the future...) and you'll NEVER EVER - even not accidentally - press the "factory reset" button, so you're free to do the update- Your jb will survive - the only thing you have to do is to re-install all kindlets via MRPI.
Gesendet von meinem Google Pixel mit Yabba-Dabba-Talk.