Android based devices from Onyx and Boyue come with native readers that support the FB2/FBZ format.
With Onyx, you can install other readers from the play store to suit your requirements. If you don't mind waiting, Onyx is releasing devices with android 6.0 support across all size ranges. Onyx is available through amazon, or through ereader.store in germany (so you don't have to deal with imports from non-EU stores, if that is an issue). See here ->
https://ereader.store/en/e-book-readers-12
That said, why don't you look at converting books into epub or other formats - Calibre works very well and fully supports the FB formats. This also opens up other device options like kindle and kobo.