I have seen some reports here of the app not working with some models of the Fire, but I have not had any problems with it myself. Both have the Logos app installed, and both have been useful as ebook readers for my Logos library. The 7 I primarily use with headphones playing my CD collection that I ripped over the years.The 8 is used more for watching youtube, twitch, etc. I currently have two Amazon Fire devices - a Fire 7 (7th Generation) and a HD 8 (8th Generation). Problem is, it'd be just so much handier if it were also good at. If ALL you'll ever want to do is Kindle & Logos, it'll do just fine. But I don't know howmuch longer I'll continue to resist.
So far, I've resisted the persistent urge to go get a real tablet (ipad? samsung? Microsoft?)& install a Kindle reader app on it.
Their implementation of typing & correction renders even a bluetooth keyboard (that does work) just as difficult to use as the e-keyboard built in.