@aleritty: If I were you I would prepare my Kindle for
firmware downgrade via diagnostics by installing
and testing (setup SSH access on you PC) Rescue Pack & Coward's rescue pack , before doing any firmware updates. So you can go back to any older firmware you like best in case you don't like new UI or have battery drain issues. Better to have all that ready and not use it, if you decide you like the new UI of fw 5.7.x.
In any case you should definitely be aware of new thing before doing the update. Things like removal of those dots indicating length of books, smaller & thinner fonts on Home screen view of new UI...