[BionicGecko]

At the moment the simplest way to avoid automatic updates on the Scribe is to put it in flight mode; there might be ways to block access to the Amazon servers directly on your router, but I wouldn’t know which addresses or domains to blacklist.

The problem with the Scribe is that so much of its core functionality relies on the Amazon cloud that it makes it quite impractical to keep it offline. Unless you only plan on writing notes on blank sheets (i.e. not in books or on PDFs) and never exporting them outside of your Scribe, you will have to let your Scribe talk to the Amazon servers at some point.

Another option is to fill your Scribe to the brim with books or personal docs, so that there isn’t enough room left to hold the update file, in which case it won’t be automatically downloaded; but this requires managing the storage so there’s still always enough room left for your notes, etc.

Personally today I don’t see a major reason to jailbreak a Kindle as many of the traditional benefits of jailbreaking (e.g. custom fonts, book cover as screen saver) are now available in the official Amazon firmware. You still need to jailbreak if you want to use an alternative reader application like KOReader, but you won’t be able to use Scribe-specific features (such as taking notes within a book) as KOReader doesn’t support them.

So it’s really up to you to see if the benefits you expect from jailbreaking outweigh the drawbacks; for what it’s worth, for the Scribe in particular, I don’t think the trade off is worth it.